Bump peter-evans/create-pull-request from 8.1.0 to 8.1.1

Bumps [peter-evans/create-pull-request](https://github.com/peter-evans/create-pull-request) from 8.1.0 to 8.1.1. - [Release notes](https://github.com/peter-evans/create-pull-request/releases) - [Commits](https://github.com/peter-evans/create-pull-request/compare/c0f553fe549906ede9cf27b5156039d195d2ece0...5f6978faf089d4d20b00c7766989d076bb2fc7f1) --- updated-dependencies: - dependency-name: peter-evans/create-pull-request dependency-version: 8.1.1 dependency-type: direct:production update-type: version-update:semver-patch ... Signed-off-by: dependabot[bot] <support@github.com>
refactor version resolving (#353 )
2026-08-08 10:17:03 +00:00 · 2026-04-13 04:58:46 +00:00 · 2026-04-12 13:44:40 +02:00 · 2026-04-11 19:14:05 +02:00 · 2026-04-11 11:41:10 +02:00 · 2026-04-10 11:34:56 +00:00
44 changed files with 66371 additions and 78062 deletions
@@ -0,0 +1,9 @@
+{
+  "compilerOptions": {
+    "module": "nodenext",
+    "moduleResolution": "nodenext",
+    "target": "es2022",
+    "types": ["node"]
+  },
+  "include": ["check-all-tests-passed-needs.ts"]
+}
@@ -17,6 +17,6 @@ jobs:
      pull-requests: read
    steps:
      - name: 🚀 Run Release Drafter
-        uses: release-drafter/release-drafter@6db134d15f3909ccc9eefd369f02bd1e9cffdf97 # v6.2.0
+        uses: release-drafter/release-drafter@5de93583980a40bd78603b6dfdcda5b4df377b32 # v7.2.0
        env:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
@@ -0,0 +1,58 @@
+name: Release
+
+on:
+  workflow_dispatch:
+    inputs:
+      version:
+        description: "Release version (e.g., 8.1.0)"
+        required: true
+        type: string
+
+permissions: {}
+
+jobs:
+  release:
+    name: Release
+    runs-on: ubuntu-latest
+    environment: release
+    permissions:
+      contents: write
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+
+      - name: Validate version
+        env:
+          VERSION: ${{ inputs.version }}
+        run: |
+          if [[ ! "$VERSION" =~ ^[0-9]+\.[0-9]+\.[0-9]+(-[a-zA-Z0-9.]+)?$ ]]; then
+            echo "::error::Version must match MAJOR.MINOR.PATCH (e.g., 8.1.0)"
+            exit 1
+          fi
+
+      - name: Publish release
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          TAG: v${{ inputs.version }}
+        run: |
+          RELEASE_JSON=$(gh release view "$TAG" --json isDraft,targetCommitish 2>&1) || {
+            echo "::error::No release found for $TAG"
+            exit 1
+          }
+
+          IS_DRAFT=$(echo "$RELEASE_JSON" | jq -r '.isDraft')
+          TARGET=$(echo "$RELEASE_JSON" | jq -r '.targetCommitish')
+
+          if [[ "$IS_DRAFT" != "true" ]]; then
+            echo "::error::Release $TAG already exists and is not a draft"
+            exit 1
+          fi
+
+          if [[ "$TARGET" != "$GITHUB_SHA" ]]; then
+            echo "::error::Draft release target ($TARGET) does not match current commit ($GITHUB_SHA)"
+            exit 1
+          fi
+
+          echo "Publishing draft release $TAG"
+          gh release edit "$TAG" --draft=false
@@ -15,22 +15,27 @@ permissions: {}
 jobs:
  lint:
    runs-on: ubuntu-latest
+    permissions:
+      security-events: write # for zizmor
    steps:
      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
        with:
          persist-credentials: false
      - name: Actionlint
-        uses: eifinger/actionlint-action@447fbfe7533062b7a9ea55f790f2396fba6d052a  # v1.10.0
+        uses: eifinger/actionlint-action@1fc89649be682d16ec5cf65ea16e269eb88d3982  # v1.10.2
+      - name: Run zizmor
+        uses: zizmorcore/zizmor-action@71321a20a9ded102f6e9ce5718a2fcec2c4f70d8 # v0.5.2
      - uses: actions/setup-node@6044e13b5dc448c55e2357c09f80417699197238 # v6.2.0
        with:
-          node-version: "20"
+          node-version-file: .nvmrc
+          cache: npm
      - run: |
          npm ci --ignore-scripts
      - run: |
          npm run all
      - name: Check all jobs are in all-tests-passed.needs
        run: |
-          tsc check-all-tests-passed-needs.ts
+          tsc -p tsconfig.json
          node check-all-tests-passed-needs.js
        working-directory: .github/scripts
      - name: Make sure no changes from linters are detected
@@ -426,6 +431,31 @@ jobs:
        env:
          RUFF_VERSION: ${{ steps.ruff-action.outputs.ruff-version }}

+  test-custom-manifest-file:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+      - name: Create test src
+        run: |
+          mkdir -p "${{ runner.temp }}/ruff-manifest-test"
+          printf 'print("hello")\n' > "${{ runner.temp }}/ruff-manifest-test/hello.py"
+      - name: Install from custom manifest file
+        id: ruff-action
+        uses: ./
+        with:
+          src: ${{ runner.temp }}/ruff-manifest-test
+          manifest-file: "https://raw.githubusercontent.com/astral-sh/ruff-action/${{ github.ref }}/__tests__/download/custom-manifest.ndjson"
+      - name: Correct version gets installed
+        run: |
+          if [ "$RUFF_VERSION" != "0.15.10" ]; then
+            echo "Wrong ruff version: $RUFF_VERSION"
+            exit 1
+          fi
+        env:
+          RUFF_VERSION: ${{ steps.ruff-action.outputs.ruff-version }}
+
  all-tests-passed:
    runs-on: ubuntu-latest
    needs:
@@ -451,6 +481,7 @@ jobs:
      - test-failure
      - test-multiple-src
      - test-parent-directory-pyproject
+      - test-custom-manifest-file
    if: always()
    steps:
      - name: All tests passed
@@ -16,15 +16,16 @@ jobs:
          persist-credentials: false
      - uses: actions/setup-node@6044e13b5dc448c55e2357c09f80417699197238 # v6.2.0
        with:
-          node-version: "20"
+          node-version-file: .nvmrc
+          cache: npm
      - name: Update known checksums
        id: update-known-checksums
        run:
-          node dist/update-known-checksums/index.js
+          node dist/update-known-checksums/index.cjs
          src/download/checksum/known-checksums.ts ${{ secrets.GITHUB_TOKEN }}
      - run: npm ci --ignore-scripts && npm run all
      - name: Create Pull Request
-        uses: peter-evans/create-pull-request@c0f553fe549906ede9cf27b5156039d195d2ece0 # v8.1.0
+        uses: peter-evans/create-pull-request@5f6978faf089d4d20b00c7766989d076bb2fc7f1 # v8.1.1
        with:
          commit-message: "chore: update known checksums"
          title:
@@ -18,7 +18,7 @@ jobs:
    steps:
      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
        with:
-          persist-credentials: false
+          persist-credentials: true
      - name: Update Major Minor Tags
        run: |
          set -x
@@ -0,0 +1 @@
+24
@@ -20,20 +20,25 @@ anything `ruff` can (ex, fix).
    - [Install a specific version](#install-a-specific-version)
    - [Install a version by supplying a semver range or pep440 specifier](#install-a-version-by-supplying-a-semver-range-or-pep440-specifier)
    - [Install a version from a specified version file](#install-a-version-from-a-specified-version-file)
+    - [Install using a custom manifest URL](#install-using-a-custom-manifest-url)
  - [Validate checksum](#validate-checksum)
  - [GitHub authentication token](#github-authentication-token)
 - [Outputs](#outputs)

 ## Usage

-| Input          | Description                                                                                                                                | Default            |
-|----------------|--------------------------------------------------------------------------------------------------------------------------------------------|--------------------|
-| `version`      | The version of Ruff to install. See [Install specific versions](#install-specific-versions)                                                | `latest`           |
-| `version-file` | The file to read the version from. See [Install a version from a specified version file](#install-a-version-from-a-specified-version-file) | None               |
-| `args`         | The arguments to pass to the `ruff` command. See [Configuring Ruff]                                                                        | `check`            |
-| `src`          | The directory or single files to run `ruff` on.                                                                                            | [github.workspace] |
-| `checksum`     | The sha256 checksum of the downloaded executable.                                                                                          | None               |
-| `github-token` | The GitHub token to use for authentication.                                                                                                | `GITHUB_TOKEN`     |
+| Input           | Description                                                                                                                                | Default            |
+|-----------------|--------------------------------------------------------------------------------------------------------------------------------------------|--------------------|
+| `version`       | The version of Ruff to install. See [Install specific versions](#install-specific-versions)                                                | discovered from `pyproject.toml`, else `latest` |
+| `version-file`  | The file to read the version from. See [Install a version from a specified version file](#install-a-version-from-a-specified-version-file) | None               |
+| `manifest-file` | URL to a custom Ruff manifest in the `astral-sh/versions` format.                                                                          | None               |
+| `args`          | The arguments to pass to the `ruff` command. See [Configuring Ruff]                                                                        | `check`            |
+| `src`           | The directory or single files to run `ruff` on.                                                                                            | [github.workspace] |
+| `checksum`      | The sha256 checksum of the downloaded artifact.                                                                                            | None               |
+| `github-token`  | The GitHub token to use when downloading Ruff release artifacts from GitHub.                                                               | `GITHUB_TOKEN`     |
+
+By default, Ruff version metadata is resolved from the
+[`astral-sh/versions` Ruff manifest](https://github.com/astral-sh/versions/blob/main/v1/ruff.ndjson).

 ### Basic

@@ -90,10 +95,10 @@ you can use the `args` input to overwrite the default value (`check`):

 ### Install specific versions

-By default this action looks for a pyproject.toml file in the root of the repository to determine
-the ruff version to install. If no pyproject.toml file is found, or no ruff version is defined in
-`project.dependencies`, `project.optional-dependencies`, or `dependency-groups`,
-the latest version is installed.
+By default this action searches upward from `src` until the workspace root to find the nearest
+`pyproject.toml` and determine the Ruff version to install. If no `pyproject.toml` file is found,
+or no Ruff version is defined in `project.dependencies`, `project.optional-dependencies`,
+`dependency-groups`, or supported Poetry dependency tables, the latest version is installed.

 > [!NOTE]
 > This action does only support ruff versions v0.0.247 and above.
@@ -146,7 +151,8 @@ to install the latest version that satisfies the range.
 #### Install a version from a specified version file

 You can specify a file to read the version from.
-Currently `pyproject.toml` and `requirements.txt` are supported.
+Currently `pyproject.toml` and `requirements.txt` are supported. If the file cannot be parsed
+or does not contain a Ruff version, the action warns and falls back to `latest`.

 ```yaml
 - name: Install a version from a specified version file
@@ -155,6 +161,26 @@ Currently `pyproject.toml` and `requirements.txt` are supported.
    version-file: "my-path/to/pyproject.toml-or-requirements.txt"
 ```

+Version resolution precedence is:
+
+1. `version`
+2. `version-file`
+3. nearest discoverable `pyproject.toml` found by searching upward from `src`
+4. `latest`
+
+#### Install using a custom manifest URL
+
+You can override the default `astral-sh/versions` manifest with `manifest-file`.
+This affects both version resolution and artifact selection.
+
+```yaml
+- name: Install Ruff from a custom manifest
+  uses: astral-sh/ruff-action@v3
+  with:
+    version: "latest"
+    manifest-file: "https://example.com/ruff.ndjson"
+```
+
 ### Validate checksum

 You can specify a checksum to validate the downloaded executable. Checksums up to the default version
@@ -171,9 +197,11 @@ are automatically verified by this action. The sha256 hashes can be found on the

 ### GitHub authentication token

-This action uses the GitHub API to fetch the ruff release artifacts. To avoid hitting the GitHub API
-rate limit too quickly, an authentication token can be provided via the `github-token` input. By
-default, the `GITHUB_TOKEN` secret is used, which is automatically provided by GitHub Actions.
+By default, this action resolves available uv versions from
+[`astral-sh/versions`](https://github.com/astral-sh/versions) and downloads release artifacts from `https://releases.astral.sh`. If this fails this action falls back to downloading from the GitHub releases page of the ruff repository.
+
+You can provide a token via `github-token` to authenticate those downloads. By default, the
+`GITHUB_TOKEN` secret is used, which is automatically provided by GitHub Actions.

 If the default
 [permissions for the GitHub token](https://docs.github.com/en/actions/security-for-github-actions/security-guides/automatic-token-authentication#permissions-for-the-github_token)
@@ -0,0 +1 @@
+{"version":"0.15.10","artifacts":[{"platform":"x86_64-unknown-linux-gnu","variant":"default","url":"https://github.com/astral-sh/ruff/releases/download/0.15.10/ruff-x86_64-unknown-linux-gnu.tar.gz","archive_format":"tar.gz","sha256":"e3e9e5c791542f00d95edc74a506e1ac24efc0af9574de01ab338187bf1ff9f6"}]}
@@ -0,0 +1,511 @@
+import { beforeEach, describe, expect, it, jest } from "@jest/globals";
+import * as semver from "semver";
+
+const mockInfo = jest.fn();
+const mockWarning = jest.fn();
+
+jest.unstable_mockModule("@actions/core", () => ({
+  debug: jest.fn(),
+  info: mockInfo,
+  warning: mockWarning,
+}));
+
+const mockDownloadTool = jest.fn();
+const mockExtractTar = jest.fn();
+const mockExtractZip = jest.fn();
+const mockCacheDir = jest.fn();
+
+jest.unstable_mockModule("@actions/tool-cache", () => ({
+  cacheDir: mockCacheDir,
+  downloadTool: mockDownloadTool,
+  evaluateVersions: (versions: string[], range: string) =>
+    semver.maxSatisfying(versions, range) ?? "",
+  extractTar: mockExtractTar,
+  extractZip: mockExtractZip,
+  find: () => "",
+  findAllVersions: () => [],
+  isExplicitVersion: (version: string) => semver.valid(version) !== null,
+}));
+
+const mockGetLatestVersion = jest.fn();
+const mockGetAllVersions = jest.fn();
+const mockGetArtifact = jest.fn();
+
+jest.unstable_mockModule("../../src/download/manifest", () => ({
+  getAllVersions: mockGetAllVersions,
+  getArtifact: mockGetArtifact,
+  getLatestVersion: mockGetLatestVersion,
+}));
+
+const mockValidateChecksum = jest.fn();
+
+jest.unstable_mockModule("../../src/download/checksum/checksum", () => ({
+  validateChecksum: mockValidateChecksum,
+}));
+
+const mockCopyFile = jest.fn();
+const mockReaddir = jest.fn();
+
+jest.unstable_mockModule("node:fs", () => ({
+  default: {},
+  promises: {
+    copyFile: mockCopyFile,
+    readdir: mockReaddir,
+  },
+}));
+
+const { downloadVersion, rewriteToMirror } = await import(
+  "../../src/download/download-version"
+);
+const { resolveVersion } = await import("../../src/version/resolve");
+
+describe("download-version", () => {
+  beforeEach(() => {
+    mockInfo.mockReset();
+    mockWarning.mockReset();
+    mockDownloadTool.mockReset();
+    mockExtractTar.mockReset();
+    mockExtractZip.mockReset();
+    mockCacheDir.mockReset();
+    mockGetLatestVersion.mockReset();
+    mockGetAllVersions.mockReset();
+    mockGetArtifact.mockReset();
+    mockValidateChecksum.mockReset();
+    mockCopyFile.mockReset();
+    mockReaddir.mockReset();
+
+    mockDownloadTool.mockResolvedValue("/tmp/downloaded");
+    mockExtractTar.mockResolvedValue("/tmp/extracted");
+    mockExtractZip.mockResolvedValue("/tmp/extracted");
+    mockCacheDir.mockResolvedValue("/tmp/cached");
+    mockReaddir.mockResolvedValue(["ruff"]);
+  });
+
+  describe("resolveVersion", () => {
+    it("uses the default manifest to resolve latest", async () => {
+      mockGetLatestVersion.mockResolvedValue("0.15.8");
+
+      const version = await resolveVersion("latest", undefined);
+
+      expect(version).toBe("0.15.8");
+      expect(mockGetLatestVersion).toHaveBeenCalledTimes(1);
+      expect(mockGetLatestVersion).toHaveBeenCalledWith(undefined);
+    });
+
+    it("uses the default manifest to resolve available versions", async () => {
+      mockGetAllVersions.mockResolvedValue(["0.15.8", "0.15.7"]);
+
+      const version = await resolveVersion("0.15.x", undefined);
+
+      expect(version).toBe("0.15.8");
+      expect(mockGetAllVersions).toHaveBeenCalledTimes(1);
+      expect(mockGetAllVersions).toHaveBeenCalledWith(undefined);
+    });
+
+    it("uses manifest-file when provided", async () => {
+      mockGetAllVersions.mockResolvedValue(["0.15.8", "0.15.7"]);
+
+      const version = await resolveVersion(
+        "0.15.x",
+        "https://example.com/custom.ndjson",
+      );
+
+      expect(version).toBe("0.15.8");
+      expect(mockGetAllVersions).toHaveBeenCalledWith(
+        "https://example.com/custom.ndjson",
+      );
+    });
+  });
+
+  describe("downloadVersion", () => {
+    it("fails when manifest lookup fails", async () => {
+      mockGetArtifact.mockRejectedValue(new Error("manifest unavailable"));
+
+      await expect(
+        downloadVersion(
+          "unknown-linux-gnu",
+          "x86_64",
+          "0.15.8",
+          undefined,
+          "token",
+        ),
+      ).rejects.toThrow("manifest unavailable");
+
+      expect(mockDownloadTool).not.toHaveBeenCalled();
+      expect(mockValidateChecksum).not.toHaveBeenCalled();
+    });
+
+    it("fails when no matching artifact exists in the default manifest", async () => {
+      mockGetArtifact.mockResolvedValue(undefined);
+
+      await expect(
+        downloadVersion(
+          "unknown-linux-gnu",
+          "x86_64",
+          "0.15.8",
+          undefined,
+          "token",
+        ),
+      ).rejects.toThrow(
+        "Could not find artifact for version 0.15.8, arch x86_64, platform unknown-linux-gnu in https://raw.githubusercontent.com/astral-sh/versions/main/v1/ruff.ndjson .",
+      );
+
+      expect(mockDownloadTool).not.toHaveBeenCalled();
+      expect(mockValidateChecksum).not.toHaveBeenCalled();
+    });
+
+    it("uses built-in checksums for default manifest downloads", async () => {
+      mockGetArtifact.mockResolvedValue({
+        archiveFormat: "tar.gz",
+        checksum: "manifest-checksum-that-should-be-ignored",
+        downloadUrl: "https://example.com/ruff.tar.gz",
+      });
+
+      await downloadVersion(
+        "unknown-linux-gnu",
+        "x86_64",
+        "0.15.8",
+        undefined,
+        "token",
+      );
+
+      expect(mockValidateChecksum).toHaveBeenCalledWith(
+        undefined,
+        "/tmp/downloaded",
+        "x86_64",
+        "unknown-linux-gnu",
+        "0.15.8",
+      );
+    });
+
+    it("rewrites GitHub Releases URLs to the Astral mirror", async () => {
+      mockGetArtifact.mockResolvedValue({
+        archiveFormat: "tar.gz",
+        checksum: "abc123",
+        downloadUrl:
+          "https://github.com/astral-sh/ruff/releases/download/0.15.8/ruff-x86_64-unknown-linux-gnu.tar.gz",
+      });
+
+      await downloadVersion(
+        "unknown-linux-gnu",
+        "x86_64",
+        "0.15.8",
+        undefined,
+        "token",
+      );
+
+      expect(mockDownloadTool).toHaveBeenCalledWith(
+        "https://releases.astral.sh/github/ruff/releases/download/0.15.8/ruff-x86_64-unknown-linux-gnu.tar.gz",
+        undefined,
+        undefined,
+      );
+    });
+
+    it("does not rewrite non-GitHub URLs", async () => {
+      mockGetArtifact.mockResolvedValue({
+        archiveFormat: "tar.gz",
+        checksum: "abc123",
+        downloadUrl: "https://example.com/ruff.tar.gz",
+      });
+
+      await downloadVersion(
+        "unknown-linux-gnu",
+        "x86_64",
+        "0.15.8",
+        undefined,
+        "token",
+      );
+
+      expect(mockDownloadTool).toHaveBeenCalledWith(
+        "https://example.com/ruff.tar.gz",
+        undefined,
+        undefined,
+      );
+    });
+
+    it("falls back to GitHub Releases when the mirror download fails", async () => {
+      mockGetArtifact.mockResolvedValue({
+        archiveFormat: "tar.gz",
+        checksum: "abc123",
+        downloadUrl:
+          "https://github.com/astral-sh/ruff/releases/download/0.15.8/ruff-x86_64-unknown-linux-gnu.tar.gz",
+      });
+
+      mockDownloadTool
+        .mockRejectedValueOnce(new Error("mirror unavailable"))
+        .mockResolvedValueOnce("/tmp/downloaded");
+
+      await downloadVersion(
+        "unknown-linux-gnu",
+        "x86_64",
+        "0.15.8",
+        undefined,
+        "token",
+      );
+
+      expect(mockDownloadTool).toHaveBeenCalledTimes(2);
+      expect(mockDownloadTool).toHaveBeenNthCalledWith(
+        1,
+        "https://releases.astral.sh/github/ruff/releases/download/0.15.8/ruff-x86_64-unknown-linux-gnu.tar.gz",
+        undefined,
+        undefined,
+      );
+      expect(mockDownloadTool).toHaveBeenNthCalledWith(
+        2,
+        "https://github.com/astral-sh/ruff/releases/download/0.15.8/ruff-x86_64-unknown-linux-gnu.tar.gz",
+        undefined,
+        "token",
+      );
+      expect(mockWarning).toHaveBeenCalledWith(
+        "Failed to download from mirror, falling back to GitHub Releases: mirror unavailable",
+      );
+    });
+
+    it("falls back to the canonical old GitHub Releases URL", async () => {
+      mockGetArtifact.mockResolvedValue({
+        archiveFormat: "tar.gz",
+        checksum: "abc123",
+        downloadUrl:
+          "https://github.com/astral-sh/ruff/releases/download/0.4.7/ruff-x86_64-unknown-linux-gnu.tar.gz",
+      });
+
+      mockDownloadTool
+        .mockRejectedValueOnce(new Error("mirror unavailable"))
+        .mockResolvedValueOnce("/tmp/downloaded");
+
+      await downloadVersion(
+        "unknown-linux-gnu",
+        "x86_64",
+        "0.4.7",
+        undefined,
+        "token",
+      );
+
+      expect(mockDownloadTool).toHaveBeenNthCalledWith(
+        2,
+        "https://github.com/astral-sh/ruff/releases/download/v0.4.7/ruff-0.4.7-x86_64-unknown-linux-gnu.tar.gz",
+        undefined,
+        "token",
+      );
+    });
+
+    it("does not fall back when checksum validation fails", async () => {
+      mockGetArtifact.mockResolvedValue({
+        archiveFormat: "tar.gz",
+        checksum: "abc123",
+        downloadUrl:
+          "https://github.com/astral-sh/ruff/releases/download/0.15.8/ruff-x86_64-unknown-linux-gnu.tar.gz",
+      });
+      mockValidateChecksum.mockRejectedValue(new Error("bad checksum"));
+
+      await expect(
+        downloadVersion(
+          "unknown-linux-gnu",
+          "x86_64",
+          "0.15.8",
+          undefined,
+          "token",
+        ),
+      ).rejects.toThrow("bad checksum");
+
+      expect(mockDownloadTool).toHaveBeenCalledTimes(1);
+      expect(mockWarning).not.toHaveBeenCalled();
+    });
+
+    it("does not fall back when extraction fails", async () => {
+      mockGetArtifact.mockResolvedValue({
+        archiveFormat: "tar.gz",
+        checksum: "abc123",
+        downloadUrl:
+          "https://github.com/astral-sh/ruff/releases/download/0.15.8/ruff-x86_64-unknown-linux-gnu.tar.gz",
+      });
+      mockExtractTar.mockRejectedValue(new Error("extract failed"));
+
+      await expect(
+        downloadVersion(
+          "unknown-linux-gnu",
+          "x86_64",
+          "0.15.8",
+          undefined,
+          "token",
+        ),
+      ).rejects.toThrow("extract failed");
+
+      expect(mockDownloadTool).toHaveBeenCalledTimes(1);
+      expect(mockWarning).not.toHaveBeenCalled();
+    });
+
+    it("does not fall back for non-GitHub URLs", async () => {
+      mockGetArtifact.mockResolvedValue({
+        archiveFormat: "tar.gz",
+        checksum: "abc123",
+        downloadUrl: "https://example.com/ruff.tar.gz",
+      });
+
+      mockDownloadTool.mockRejectedValue(new Error("download failed"));
+
+      await expect(
+        downloadVersion(
+          "unknown-linux-gnu",
+          "x86_64",
+          "0.15.8",
+          undefined,
+          "token",
+        ),
+      ).rejects.toThrow("download failed");
+
+      expect(mockDownloadTool).toHaveBeenCalledTimes(1);
+    });
+
+    it("uses manifest-file checksum metadata when checksum input is unset", async () => {
+      mockGetArtifact.mockResolvedValue({
+        archiveFormat: "tar.gz",
+        checksum: "manifest-checksum",
+        downloadUrl: "https://example.com/custom-ruff.tar.gz",
+      });
+
+      await downloadVersion(
+        "unknown-linux-gnu",
+        "x86_64",
+        "0.15.8",
+        "",
+        "token",
+        "https://example.com/custom.ndjson",
+      );
+
+      expect(mockValidateChecksum).toHaveBeenCalledWith(
+        "manifest-checksum",
+        "/tmp/downloaded",
+        "x86_64",
+        "unknown-linux-gnu",
+        "0.15.8",
+      );
+    });
+
+    it("prefers checksum input over manifest-file checksum metadata", async () => {
+      mockGetArtifact.mockResolvedValue({
+        archiveFormat: "tar.gz",
+        checksum: "manifest-checksum",
+        downloadUrl: "https://example.com/custom-ruff.tar.gz",
+      });
+
+      await downloadVersion(
+        "unknown-linux-gnu",
+        "x86_64",
+        "0.15.8",
+        "user-checksum",
+        "token",
+        "https://example.com/custom.ndjson",
+      );
+
+      expect(mockValidateChecksum).toHaveBeenCalledWith(
+        "user-checksum",
+        "/tmp/downloaded",
+        "x86_64",
+        "unknown-linux-gnu",
+        "0.15.8",
+      );
+    });
+
+    it("preserves tar extraction behavior for newer versions", async () => {
+      mockGetArtifact.mockResolvedValue({
+        archiveFormat: "tar.gz",
+        checksum: "abc123",
+        downloadUrl: "https://example.com/ruff.tar.gz",
+      });
+
+      await downloadVersion(
+        "unknown-linux-gnu",
+        "x86_64",
+        "0.15.8",
+        "user-checksum",
+        "token",
+      );
+
+      expect(mockExtractTar).toHaveBeenCalledWith("/tmp/downloaded");
+      expect(mockCacheDir).toHaveBeenCalledWith(
+        "/tmp/extracted/ruff-x86_64-unknown-linux-gnu",
+        "ruff",
+        "0.15.8",
+        "x86_64",
+      );
+    });
+
+    it("preserves tar extraction behavior for older versions", async () => {
+      mockGetArtifact.mockResolvedValue({
+        archiveFormat: "tar.gz",
+        checksum: "abc123",
+        downloadUrl: "https://example.com/ruff.tar.gz",
+      });
+
+      await downloadVersion(
+        "unknown-linux-gnu",
+        "x86_64",
+        "0.4.10",
+        undefined,
+        "token",
+      );
+
+      expect(mockCacheDir).toHaveBeenCalledWith(
+        "/tmp/extracted",
+        "ruff",
+        "0.4.10",
+        "x86_64",
+      );
+    });
+
+    it("preserves zip extraction behavior on Windows", async () => {
+      mockGetArtifact.mockResolvedValue({
+        archiveFormat: "zip",
+        checksum: "abc123",
+        downloadUrl: "https://example.com/ruff.zip",
+      });
+
+      await downloadVersion(
+        "pc-windows-msvc",
+        "x86_64",
+        "0.15.8",
+        undefined,
+        "token",
+      );
+
+      expect(mockCopyFile).toHaveBeenCalledWith(
+        "/tmp/downloaded",
+        "/tmp/downloaded.zip",
+      );
+      expect(mockExtractZip).toHaveBeenCalledWith("/tmp/downloaded.zip");
+      expect(mockCacheDir).toHaveBeenCalledWith(
+        "/tmp/extracted",
+        "ruff",
+        "0.15.8",
+        "x86_64",
+      );
+    });
+  });
+
+  describe("rewriteToMirror", () => {
+    it("rewrites a GitHub Releases URL to the Astral mirror", () => {
+      expect(
+        rewriteToMirror(
+          "https://github.com/astral-sh/ruff/releases/download/0.15.8/ruff-x86_64-unknown-linux-gnu.tar.gz",
+        ),
+      ).toBe(
+        "https://releases.astral.sh/github/ruff/releases/download/0.15.8/ruff-x86_64-unknown-linux-gnu.tar.gz",
+      );
+    });
+
+    it("returns undefined for non-GitHub URLs", () => {
+      expect(
+        rewriteToMirror("https://example.com/ruff.tar.gz"),
+      ).toBeUndefined();
+    });
+
+    it("returns undefined for a different GitHub repo", () => {
+      expect(
+        rewriteToMirror(
+          "https://github.com/other/repo/releases/download/v1.0/file.tar.gz",
+        ),
+      ).toBeUndefined();
+    });
+  });
+});
@@ -0,0 +1,196 @@
+import { beforeEach, describe, expect, it, jest } from "@jest/globals";
+
+const mockFetch = jest.fn();
+
+jest.unstable_mockModule("@actions/core", () => ({
+  debug: jest.fn(),
+  info: jest.fn(),
+}));
+
+jest.unstable_mockModule("../../src/utils/fetch", () => ({
+  fetch: mockFetch,
+}));
+
+const {
+  clearManifestCache,
+  fetchManifest,
+  getAllVersions,
+  getArtifact,
+  getLatestVersion,
+  parseManifest,
+} = await import("../../src/download/manifest");
+
+const sampleManifestResponse = `{"version":"0.15.8","artifacts":[{"platform":"aarch64-apple-darwin","variant":"default","url":"https://github.com/astral-sh/ruff/releases/download/0.15.8/ruff-aarch64-apple-darwin.tar.gz","archive_format":"tar.gz","sha256":"fcf0a9ea6599c6ae28a4c854ac6da76f2c889354d7c36ce136ef071f7ab9721f"},{"platform":"x86_64-pc-windows-msvc","variant":"default","url":"https://github.com/astral-sh/ruff/releases/download/0.15.8/ruff-x86_64-pc-windows-msvc.zip","archive_format":"zip","sha256":"eb02fd95d8e0eed462b4a67ecdd320d865b38c560bffcda9a0b87ec944bdf036"}]}
+{"version":"0.15.7","artifacts":[{"platform":"aarch64-apple-darwin","variant":"default","url":"https://github.com/astral-sh/ruff/releases/download/0.15.7/ruff-aarch64-apple-darwin.tar.gz","archive_format":"tar.gz","sha256":"606b3c6949d971709f2526fa0d9f0fd23ccf60e09f117999b406b424af18a6a6"}]}`;
+
+const multiVariantManifestResponse = `{"version":"0.15.8","artifacts":[{"platform":"aarch64-apple-darwin","variant":"python-managed","url":"https://github.com/astral-sh/ruff/releases/download/0.15.8/ruff-aarch64-apple-darwin-managed.tar.gz","archive_format":"tar.gz","sha256":"managed-checksum"},{"platform":"aarch64-apple-darwin","variant":"default","url":"https://github.com/astral-sh/ruff/releases/download/0.15.8/ruff-aarch64-apple-darwin.zip","archive_format":"zip","sha256":"default-checksum"}]}`;
+
+const oldVersionManifestResponse = `{"version":"v0.4.7","artifacts":[{"platform":"0.4.7-aarch64-apple-darwin","variant":"default","url":"https://github.com/astral-sh/ruff/releases/download/v0.4.7/ruff-0.4.7-aarch64-apple-darwin.tar.gz","archive_format":"tar.gz","sha256":"old-checksum"}]}`;
+
+function createMockResponse(
+  ok: boolean,
+  status: number,
+  statusText: string,
+  data: string,
+) {
+  return {
+    ok,
+    status,
+    statusText,
+    text: async () => data,
+  };
+}
+
+describe("manifest", () => {
+  beforeEach(() => {
+    clearManifestCache();
+    mockFetch.mockReset();
+  });
+
+  describe("fetchManifest", () => {
+    it("fetches and parses manifest data", async () => {
+      mockFetch.mockResolvedValue(
+        createMockResponse(true, 200, "OK", sampleManifestResponse),
+      );
+
+      const versions = await fetchManifest();
+
+      expect(versions).toHaveLength(2);
+      expect(versions[0]?.version).toBe("0.15.8");
+      expect(versions[1]?.version).toBe("0.15.7");
+    });
+
+    it("throws on a failed fetch", async () => {
+      mockFetch.mockResolvedValue(
+        createMockResponse(false, 500, "Internal Server Error", ""),
+      );
+
+      await expect(fetchManifest()).rejects.toThrow(
+        "Failed to fetch manifest data: 500 Internal Server Error",
+      );
+    });
+
+    it("caches results per URL", async () => {
+      mockFetch.mockResolvedValue(
+        createMockResponse(true, 200, "OK", sampleManifestResponse),
+      );
+
+      await fetchManifest("https://example.com/custom.ndjson");
+      await fetchManifest("https://example.com/custom.ndjson");
+
+      expect(mockFetch).toHaveBeenCalledTimes(1);
+    });
+  });
+
+  describe("getAllVersions", () => {
+    it("returns all version strings", async () => {
+      mockFetch.mockResolvedValue(
+        createMockResponse(true, 200, "OK", sampleManifestResponse),
+      );
+
+      const versions = await getAllVersions(
+        "https://example.com/custom.ndjson",
+      );
+
+      expect(versions).toEqual(["0.15.8", "0.15.7"]);
+    });
+  });
+
+  describe("getLatestVersion", () => {
+    it("returns the first version string", async () => {
+      mockFetch.mockResolvedValue(
+        createMockResponse(true, 200, "OK", sampleManifestResponse),
+      );
+
+      await expect(
+        getLatestVersion("https://example.com/custom.ndjson"),
+      ).resolves.toBe("0.15.8");
+    });
+  });
+
+  describe("getArtifact", () => {
+    beforeEach(() => {
+      mockFetch.mockResolvedValue(
+        createMockResponse(true, 200, "OK", sampleManifestResponse),
+      );
+    });
+
+    it("finds an artifact by version and platform", async () => {
+      const artifact = await getArtifact("0.15.8", "aarch64", "apple-darwin");
+
+      expect(artifact).toEqual({
+        archiveFormat: "tar.gz",
+        checksum:
+          "fcf0a9ea6599c6ae28a4c854ac6da76f2c889354d7c36ce136ef071f7ab9721f",
+        downloadUrl:
+          "https://github.com/astral-sh/ruff/releases/download/0.15.8/ruff-aarch64-apple-darwin.tar.gz",
+      });
+    });
+
+    it("finds a windows artifact", async () => {
+      const artifact = await getArtifact("0.15.8", "x86_64", "pc-windows-msvc");
+
+      expect(artifact).toEqual({
+        archiveFormat: "zip",
+        checksum:
+          "eb02fd95d8e0eed462b4a67ecdd320d865b38c560bffcda9a0b87ec944bdf036",
+        downloadUrl:
+          "https://github.com/astral-sh/ruff/releases/download/0.15.8/ruff-x86_64-pc-windows-msvc.zip",
+      });
+    });
+
+    it("prefers the default variant when multiple artifacts share a platform", async () => {
+      mockFetch.mockResolvedValue(
+        createMockResponse(true, 200, "OK", multiVariantManifestResponse),
+      );
+
+      const artifact = await getArtifact("0.15.8", "aarch64", "apple-darwin");
+
+      expect(artifact).toEqual({
+        archiveFormat: "zip",
+        checksum: "default-checksum",
+        downloadUrl:
+          "https://github.com/astral-sh/ruff/releases/download/0.15.8/ruff-aarch64-apple-darwin.zip",
+      });
+    });
+
+    it("finds an old artifact when the manifest version has a v prefix", async () => {
+      mockFetch.mockResolvedValue(
+        createMockResponse(true, 200, "OK", oldVersionManifestResponse),
+      );
+
+      const artifact = await getArtifact("0.4.7", "aarch64", "apple-darwin");
+
+      expect(artifact).toEqual({
+        archiveFormat: "tar.gz",
+        checksum: "old-checksum",
+        downloadUrl:
+          "https://github.com/astral-sh/ruff/releases/download/v0.4.7/ruff-0.4.7-aarch64-apple-darwin.tar.gz",
+      });
+    });
+
+    it("returns undefined for an unknown version", async () => {
+      const artifact = await getArtifact("0.0.1", "aarch64", "apple-darwin");
+
+      expect(artifact).toBeUndefined();
+    });
+
+    it("returns undefined for an unknown platform", async () => {
+      const artifact = await getArtifact(
+        "0.15.8",
+        "aarch64",
+        "unknown-linux-musl",
+      );
+
+      expect(artifact).toBeUndefined();
+    });
+  });
+
+  describe("parseManifest", () => {
+    it("throws for malformed manifest data", () => {
+      expect(() => parseManifest('{"version":"0.1.0"', "test-source")).toThrow(
+        "Failed to parse manifest data from test-source",
+      );
+    });
+  });
+});
@@ -0,0 +1,122 @@
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+import { beforeEach, describe, expect, it, jest } from "@jest/globals";
+
+const debug = jest.fn();
+const info = jest.fn();
+
+jest.unstable_mockModule("@actions/core", () => ({
+  debug,
+  info,
+}));
+
+const { findPyprojectToml } = await import("../../src/utils/pyproject-finder");
+
+const testFilePath = fileURLToPath(import.meta.url);
+const testDir = path.dirname(testFilePath);
+const repoRoot = path.resolve(testDir, "..", "..");
+const fixturesDir = path.join(repoRoot, "__tests__", "fixtures");
+
+describe("findPyprojectToml", () => {
+  beforeEach(() => {
+    debug.mockReset();
+    info.mockReset();
+  });
+
+  describe("when pyproject.toml exists in src directory", () => {
+    it("should return the exact path", () => {
+      const result = findPyprojectToml(fixturesDir, repoRoot);
+
+      expect(result).toContain("pyproject.toml");
+      expect(result).toContain("fixtures");
+      expect(info).toHaveBeenCalled();
+    });
+  });
+
+  describe("when pyproject.toml exists only in parent directory", () => {
+    it("should search upwards and find the parent's pyproject.toml", () => {
+      const subprojectDir = path.join(
+        fixturesDir,
+        "parent-config-project",
+        "subproject",
+      );
+
+      const result = findPyprojectToml(subprojectDir, repoRoot);
+
+      expect(result).toBeTruthy();
+      expect(result).toContain("pyproject.toml");
+      expect(result).toContain("parent-config-project");
+      expect(info).toHaveBeenCalled();
+    });
+  });
+
+  describe("boundary conditions", () => {
+    it("should stop searching at workspace root and return undefined when not found", () => {
+      const nodeModulesDir = path.join(repoRoot, "node_modules", "@actions");
+
+      const result = findPyprojectToml(nodeModulesDir, repoRoot);
+
+      expect(result).toBeUndefined();
+      expect(info).not.toHaveBeenCalledWith(
+        expect.stringContaining("Found pyproject.toml"),
+      );
+    });
+
+    it("should find pyproject.toml when it exists at workspace root", () => {
+      const parentConfigProjectDir = path.join(
+        fixturesDir,
+        "parent-config-project",
+      );
+      const subprojectDir = path.join(parentConfigProjectDir, "subproject");
+
+      const result = findPyprojectToml(subprojectDir, parentConfigProjectDir);
+
+      expect(result).toBeTruthy();
+      expect(result).toContain("pyproject.toml");
+      expect(result).toContain("parent-config-project");
+    });
+
+    it("should stop at workspace root even if searching from it", () => {
+      const result = findPyprojectToml(fixturesDir, fixturesDir);
+
+      expect(result).toBeTruthy();
+      expect(result).toContain("pyproject.toml");
+      expect(result).toContain("fixtures");
+    });
+  });
+
+  describe("edge cases", () => {
+    it("should handle relative paths", () => {
+      const result = findPyprojectToml("./__tests__/fixtures", ".");
+
+      expect(result).toBeTruthy();
+      expect(result).toContain("pyproject.toml");
+    });
+
+    it("should handle when src equals workspace root", () => {
+      const result = findPyprojectToml(fixturesDir, fixturesDir);
+
+      expect(result).toBeTruthy();
+      expect(result).toContain("pyproject.toml");
+      expect(result).toContain("fixtures");
+    });
+
+    it("should log debug messages for each checked path", () => {
+      const pythonProjectDir = path.join(fixturesDir, "python-project");
+
+      findPyprojectToml(pythonProjectDir, repoRoot);
+
+      expect(debug).toHaveBeenCalled();
+      expect(debug.mock.calls.length).toBeGreaterThan(0);
+      expect(debug.mock.calls[0][0]).toContain("Checking for");
+      expect(debug.mock.calls[0][0]).toContain("python-project");
+    });
+
+    it("should handle paths with trailing slashes", () => {
+      const result = findPyprojectToml(`${fixturesDir}/`, repoRoot);
+
+      expect(result).toBeTruthy();
+      expect(result).toContain("pyproject.toml");
+    });
+  });
+});
@@ -0,0 +1,128 @@
+import { beforeEach, describe, expect, it, jest } from "@jest/globals";
+
+const info = jest.fn();
+const warning = jest.fn();
+
+jest.unstable_mockModule("@actions/core", () => ({
+  debug: jest.fn(),
+  info,
+  warning,
+}));
+
+const { findRuffVersionInSpec, getRuffVersionFromFile } = await import(
+  "../../src/version/file-parser"
+);
+
+describe("file-parser", () => {
+  beforeEach(() => {
+    info.mockReset();
+    warning.mockReset();
+  });
+
+  describe("findRuffVersionInSpec", () => {
+    it("extracts version from 'ruff==0.9.3'", () => {
+      const result = findRuffVersionInSpec("ruff==0.9.3");
+      expect(result).toBe("0.9.3");
+      expect(info).toHaveBeenCalledWith(
+        "Found ruff version in requirements file: 0.9.3",
+      );
+      expect(warning).not.toHaveBeenCalled();
+    });
+
+    it("extracts version from 'ruff>=0.14'", () => {
+      const result = findRuffVersionInSpec("ruff>=0.14");
+      expect(result).toBe(">=0.14");
+      expect(warning).not.toHaveBeenCalled();
+    });
+
+    it("extracts version from 'ruff ~=1.0.0'", () => {
+      const result = findRuffVersionInSpec("ruff ~=1.0.0");
+      expect(result).toBe("~=1.0.0");
+      expect(warning).not.toHaveBeenCalled();
+    });
+
+    it("extracts version from 'ruff>=0.14,<1.0'", () => {
+      const result = findRuffVersionInSpec("ruff>=0.14,<1.0");
+      expect(result).toBe(">=0.14,<1.0");
+      expect(warning).not.toHaveBeenCalled();
+    });
+
+    it("extracts version from 'ruff>=0.14,<2.0,!=1.5.0'", () => {
+      const result = findRuffVersionInSpec("ruff>=0.14,<2.0,!=1.5.0");
+      expect(result).toBe(">=0.14,<2.0,!=1.5.0");
+      expect(warning).not.toHaveBeenCalled();
+    });
+
+    it("returns undefined for non-ruff dependencies", () => {
+      const result = findRuffVersionInSpec("another-dep==0.1.6");
+      expect(result).toBeUndefined();
+      expect(info).not.toHaveBeenCalled();
+      expect(warning).not.toHaveBeenCalled();
+    });
+
+    it("strips trailing backslash", () => {
+      const result = findRuffVersionInSpec("ruff==0.9.3 \\");
+      expect(result).toBe("0.9.3");
+      expect(info).toHaveBeenCalledWith(
+        "Found ruff version in requirements file: 0.9.3",
+      );
+      expect(warning).not.toHaveBeenCalled();
+    });
+
+    it("strips environment markers and warns", () => {
+      const result = findRuffVersionInSpec(
+        'ruff>=0.14 ; python_version >= "3.11"',
+      );
+      expect(result).toBe(">=0.14");
+      expect(info).toHaveBeenCalledWith(
+        "Found ruff version in requirements file: >=0.14",
+      );
+      expect(warning).toHaveBeenCalledWith(
+        "Environment markers are ignored. ruff is a standalone tool that works independently of Python version.",
+      );
+    });
+
+    it("handles whitespace", () => {
+      const result = findRuffVersionInSpec("  ruff  >=0.14  ");
+      expect(result).toBe(">=0.14");
+      expect(warning).not.toHaveBeenCalled();
+    });
+
+    it("returns undefined for empty strings", () => {
+      const result = findRuffVersionInSpec("");
+      expect(result).toBeUndefined();
+      expect(info).not.toHaveBeenCalled();
+      expect(warning).not.toHaveBeenCalled();
+    });
+  });
+
+  describe("getRuffVersionFromFile", () => {
+    it("reads the version from requirements.txt", () => {
+      const result = getRuffVersionFromFile(
+        "__tests__/fixtures/requirements.txt",
+      );
+      expect(result).toBe("0.9.0");
+    });
+
+    it("reads the version from requirements files with hashes", () => {
+      const result = getRuffVersionFromFile(
+        "__tests__/fixtures/requirements-with-hash.txt",
+      );
+      expect(result).toBe("0.9.0");
+    });
+
+    it("reads the version from pyproject.toml dependencies", () => {
+      const result = getRuffVersionFromFile(
+        "__tests__/fixtures/pyproject.toml",
+      );
+      expect(result).toBe("0.9.3");
+    });
+
+    it("reads the version from Poetry dependencies", () => {
+      const result = getRuffVersionFromFile(
+        "__tests__/fixtures/pyproject-dependency-poetry-project/pyproject.toml",
+      );
+      expect(result).toBe("~0.8.2");
+    });
+  });
+});
@@ -0,0 +1,164 @@
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import {
+  afterEach,
+  beforeEach,
+  describe,
+  expect,
+  it,
+  jest,
+} from "@jest/globals";
+
+const debug = jest.fn();
+const info = jest.fn();
+const warning = jest.fn();
+
+jest.unstable_mockModule("@actions/core", () => ({
+  debug,
+  info,
+  warning,
+}));
+
+const { resolveVersionRequest } = await import(
+  "../../src/version/version-request-resolver"
+);
+
+const tempDirs: string[] = [];
+
+function createTempProject(files: Record<string, string> = {}): string {
+  const dir = fs.mkdtempSync(
+    path.join(os.tmpdir(), "ruff-action-version-test-"),
+  );
+  tempDirs.push(dir);
+
+  for (const [relativePath, content] of Object.entries(files)) {
+    const filePath = path.join(dir, relativePath);
+    fs.mkdirSync(path.dirname(filePath), { recursive: true });
+    fs.writeFileSync(filePath, content);
+  }
+
+  return dir;
+}
+
+afterEach(() => {
+  for (const dir of tempDirs.splice(0)) {
+    fs.rmSync(dir, { force: true, recursive: true });
+  }
+});
+
+describe("resolveVersionRequest", () => {
+  beforeEach(() => {
+    debug.mockReset();
+    info.mockReset();
+    warning.mockReset();
+  });
+
+  it("prefers explicit input over workspace discovery", () => {
+    const workspaceRoot = createTempProject({
+      "pyproject.toml": `[project]\ndependencies = ["ruff==0.5.14"]\n`,
+    });
+
+    const request = resolveVersionRequest({
+      sourceDirectory: workspaceRoot,
+      version: "==0.6.0",
+      workspaceRoot,
+    });
+
+    expect(request).toEqual({
+      source: "input",
+      specifier: "0.6.0",
+    });
+  });
+
+  it("uses requirements.txt when it is passed via version-file", () => {
+    const workspaceRoot = createTempProject({
+      "requirements.txt": "ruff==0.6.17\nruff-api==0.1.0\n",
+    });
+
+    const request = resolveVersionRequest({
+      sourceDirectory: workspaceRoot,
+      versionFile: path.join(workspaceRoot, "requirements.txt"),
+      workspaceRoot,
+    });
+
+    expect(request).toEqual({
+      format: "requirements",
+      source: "version-file",
+      sourcePath: path.join(workspaceRoot, "requirements.txt"),
+      specifier: "0.6.17",
+    });
+  });
+
+  it("warns and falls back to latest when version-file does not resolve a version", () => {
+    const workspaceRoot = createTempProject({
+      "requirements.txt": "ruff-api==0.1.0\n",
+    });
+
+    const request = resolveVersionRequest({
+      sourceDirectory: workspaceRoot,
+      versionFile: path.join(workspaceRoot, "requirements.txt"),
+      workspaceRoot,
+    });
+
+    expect(request).toEqual({
+      source: "default",
+      specifier: "latest",
+    });
+    expect(warning).toHaveBeenCalledWith(
+      `Could not parse version from ${path.join(workspaceRoot, "requirements.txt")}. Using latest version.`,
+    );
+  });
+
+  it("discovers pyproject.toml by searching upward from src", () => {
+    const workspaceRoot = createTempProject({
+      "pyproject.toml": `[project]\ndependencies = ["ruff==0.10.0"]\n`,
+      "subproject/nested/example.py": 'print("hello")\n',
+    });
+    const sourceDirectory = path.join(workspaceRoot, "subproject", "nested");
+
+    const request = resolveVersionRequest({
+      sourceDirectory,
+      workspaceRoot,
+    });
+
+    expect(request).toEqual({
+      format: "pyproject.toml",
+      source: "pyproject.toml",
+      sourcePath: path.join(workspaceRoot, "pyproject.toml"),
+      specifier: "0.10.0",
+    });
+  });
+
+  it("falls back to latest when no workspace version source is found", () => {
+    const workspaceRoot = createTempProject({
+      "subproject/example.py": 'print("hello")\n',
+    });
+
+    const request = resolveVersionRequest({
+      sourceDirectory: path.join(workspaceRoot, "subproject"),
+      workspaceRoot,
+    });
+
+    expect(request).toEqual({
+      source: "default",
+      specifier: "latest",
+    });
+    expect(info).toHaveBeenCalledWith(
+      "Could not find pyproject.toml. Using latest version.",
+    );
+  });
+
+  it("throws when both version and version-file are specified", () => {
+    const workspaceRoot = createTempProject();
+
+    expect(() =>
+      resolveVersionRequest({
+        sourceDirectory: workspaceRoot,
+        version: "0.6.0",
+        versionFile: path.join(workspaceRoot, "requirements.txt"),
+        workspaceRoot,
+      }),
+    ).toThrow("It is not allowed to specify both version and version-file");
+  });
+});
@@ -11,27 +11,29 @@ inputs:
    required: false
    default: ${{ github.workspace }}
  version:
-    description: "The version of Ruff to use, e.g., `0.6.0` Defaults to the version in pyproject.toml or 'latest'."
+    description: "The version of Ruff to use, e.g., `0.6.0`. Defaults to the first discoverable version in pyproject.toml searched upward from `src`, or `latest`."
    required: false
    default: ""
  version-file:
-    description: "Path to a pyproject.toml or requirements.txt file to read the version from."
+    description: "Path to a pyproject.toml or requirements.txt file to read the version from. If parsing fails, the action warns and falls back to `latest`."
    required: false
  checksum:
    description: "The checksum of the ruff version to install"
    required: false
+  manifest-file:
+    description: "URL to a custom manifest file in the astral-sh/versions format."
+    required: false
  github-token:
    description:
-      "Used to increase the rate limit when retrieving versions and downloading
-      ruff."
+      "Used for authenticated downloads of Ruff release artifacts from GitHub."
    required: false
    default: ${{ github.token }}
 outputs:
  ruff-version:
    description: "The installed ruff version. Useful when using latest."
 runs:
-  using: "node20"
-  main: "dist/ruff-action/index.js"
+  using: "node24"
+  main: "dist/ruff-action/index.cjs"
 branding:
  icon: "code"
  color: "black"
@@ -1,5 +1,5 @@
 {
-  "$schema": "https://biomejs.dev/schemas/2.3.2/schema.json",
+  "$schema": "https://biomejs.dev/schemas/2.4.9/schema.json",
  "assist": {
    "actions": {
      "source": {
@@ -1,12 +0,0 @@
-/** @type {import('ts-jest').JestConfigWithTsJest} */
-module.exports = {
-  collectCoverageFrom: ["src/**/*.ts", "!src/**/*.d.ts"],
-  moduleFileExtensions: ["ts", "js"],
-  preset: "ts-jest",
-  roots: ["<rootDir>/src"],
-  testEnvironment: "node",
-  testMatch: ["**/*.test.ts"],
-  transform: {
-    "^.+\\.ts$": "ts-jest",
-  },
-};
@@ -0,0 +1,12 @@
+import { createDefaultEsmPreset } from "ts-jest";
+
+const preset = createDefaultEsmPreset();
+
+/** @type {import('jest').Config} */
+export default {
+  ...preset,
+  collectCoverageFrom: ["src/**/*.ts", "!src/**/*.d.ts"],
+  moduleFileExtensions: ["ts", "js", "mjs"],
+  testEnvironment: "node",
+  testMatch: ["<rootDir>/__tests__/**/*.test.ts"],
+};
@@ -2,16 +2,18 @@
  "name": "ruff-action",
  "version": "1.0.0",
  "private": true,
+  "type": "module",
  "description": "A GitHub Action to run Ruff, an extremely fast Python linter and code formatter.",
-  "main": "dist/ruff-action/index.js",
+  "main": "dist/ruff-action/index.cjs",
  "scripts": {
-    "build": "tsc",
+    "build": "tsc --noEmit",
    "check": "biome check --write",
-    "package": "ncc build -o dist/ruff-action src/ruff-action.ts && ncc build -o dist/update-known-checksums src/update-known-checksums.ts",
+    "package": "node scripts/build-dist.mjs",
    "act": "act pull_request -W .github/workflows/test.yml --container-architecture linux/amd64 -s GITHUB_TOKEN=\"$(gh auth token)\"",
-    "update-known-checksums": "RUNNER_TEMP=known_checksums node dist/update-known-checksums/index.js src/download/checksum/known-checksums.ts \"$(gh auth token)\"",
-    "test": "jest",
-    "all": "npm ci --ignore-scripts && npm run build && npm run check && npm run test && npm run package"
+    "update-known-checksums": "RUNNER_TEMP=known_checksums node dist/update-known-checksums/index.cjs src/download/checksum/known-checksums.ts \"$(gh auth token)\"",
+    "test:unit": "node --experimental-vm-modules ./node_modules/jest/bin/jest.js",
+    "test": "npm run build && npm run test:unit",
+    "all": "npm run build && npm run check && npm run package && npm run test:unit"
  },
  "repository": {
    "type": "git",
@@ -26,25 +28,26 @@
  "author": "@eifinger",
  "license": "Apache-2.0",
  "dependencies": {
-    "@actions/core": "^1.11.1",
-    "@actions/exec": "^1.1.1",
-    "@actions/tool-cache": "^2.0.2",
+    "@actions/core": "^3.0.0",
+    "@actions/exec": "^3.0.0",
+    "@actions/tool-cache": "^4.0.0",
    "@octokit/core": "^7.0.3",
    "@octokit/plugin-paginate-rest": "^13.1.1",
    "@octokit/plugin-rest-endpoint-methods": "^16.0.0",
    "@renovatebot/pep440": "^4.2.1",
-    "smol-toml": "^1.6.0"
+    "smol-toml": "^1.6.0",
+    "undici": "^6.24.1"
  },
  "devDependencies": {
-    "@biomejs/biome": "2.3.2",
+    "@biomejs/biome": "^2.4.7",
    "@types/jest": "^29.5.14",
    "@types/js-yaml": "^4.0.9",
-    "@types/node": "^24.10.9",
+    "@types/node": "^25.5.0",
    "@types/semver": "^7.7.1",
-    "@vercel/ncc": "^0.38.3",
-    "jest": "^29.7.0",
-    "js-yaml": "^4.1.0",
-    "ts-jest": "^29.2.5",
-    "typescript": "^5.9.2"
+    "esbuild": "^0.27.4",
+    "jest": "^30.3.0",
+    "js-yaml": "^4.1.1",
+    "ts-jest": "^29.4.6",
+    "typescript": "^5.9.3"
  }
 }
@@ -0,0 +1,41 @@
+import { mkdir, rm } from "node:fs/promises";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+import { build } from "esbuild";
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+const repoRoot = path.resolve(__dirname, "..");
+
+const builds = [
+  {
+    entryPoint: path.join(repoRoot, "src", "ruff-action.ts"),
+    outfile: path.join(repoRoot, "dist", "ruff-action", "index.cjs"),
+    staleOutfile: path.join(repoRoot, "dist", "ruff-action", "index.js"),
+  },
+  {
+    entryPoint: path.join(repoRoot, "src", "update-known-checksums.ts"),
+    outfile: path.join(repoRoot, "dist", "update-known-checksums", "index.cjs"),
+    staleOutfile: path.join(
+      repoRoot,
+      "dist",
+      "update-known-checksums",
+      "index.js",
+    ),
+  },
+];
+
+await Promise.all(
+  builds.map(async ({ entryPoint, outfile, staleOutfile }) => {
+    await rm(staleOutfile, { force: true });
+    await mkdir(path.dirname(outfile), { recursive: true });
+    await build({
+      bundle: true,
+      entryPoints: [entryPoint],
+      format: "cjs",
+      outfile,
+      platform: "node",
+      target: "node24",
+    });
+  }),
+);
@@ -1,5 +1,379 @@
 // AUTOGENERATED_DO_NOT_EDIT
 export const KNOWN_CHECKSUMS: { [key: string]: string } = {
+  "aarch64-apple-darwin-0.15.10":
+    "77c1df502dcfaaec52c6ce203b504b8554c88ab66ac01313410fa68ad9aafd5b",
+  "aarch64-pc-windows-msvc-0.15.10":
+    "1776bf104277b3fbb3b3e4b481655f492f6df10210e2e00cd94132e66e999bd4",
+  "aarch64-unknown-linux-gnu-0.15.10":
+    "b775a5a09484549ac3fd377b5ce34955cf633165169671d1c4a215c113ce15df",
+  "aarch64-unknown-linux-musl-0.15.10":
+    "84754f0e58f58fb123ea49b8d22b8ce2cc96e4046b7c1b1ed99f6af7fe76f8ef",
+  "arm-unknown-linux-musleabihf-0.15.10":
+    "e94eb3061a263217fad7219a0b20e5a746a31f44387cd21c31eb5103357dbb8c",
+  "armv7-unknown-linux-gnueabihf-0.15.10":
+    "7a348dd60f4c5563482504acabba49def8a8cd5d957b6e145a1dbdef7cdf0663",
+  "armv7-unknown-linux-musleabihf-0.15.10":
+    "8c85562d2ed09bc4edbbea151aec386e8f7e9f5499e6c5d0324fd26fe7c5dc8a",
+  "i686-pc-windows-msvc-0.15.10":
+    "a8b4132914f197d1fef5f48fd7f0f8e840546a814daf9f680109344407da79ac",
+  "i686-unknown-linux-gnu-0.15.10":
+    "6f9b23d07d90ef3ac148c8b81fc8ea37647f1241e4db18be1b0a24df43d479f8",
+  "i686-unknown-linux-musl-0.15.10":
+    "63d80b9427a8299c8bf08d34621e187fe5fe5f696f36b54635e00248d3ca7e5f",
+  "powerpc64le-unknown-linux-gnu-0.15.10":
+    "49cfcb83828844f61e00c643dd81182a015140b9bf58cee5b115f705e99749e6",
+  "riscv64gc-unknown-linux-gnu-0.15.10":
+    "8d7eeef9d9abd9e88b92d9420021be5fbd1dbd60e10ef7f989060213cd68c4c7",
+  "s390x-unknown-linux-gnu-0.15.10":
+    "80056787672af7b4e9217afdd666a8c19eebbe5eb2fe626a6a9a779ea6778a1b",
+  "x86_64-apple-darwin-0.15.10":
+    "7210e06196de876771cc0bad0f1d57678e709d039f184b491fdaa600d6a95a5e",
+  "x86_64-pc-windows-msvc-0.15.10":
+    "6f8f9a445102107ee3c0a05c8f386bacb32238199ecbc0983b9b06c5ea3d7c5e",
+  "x86_64-unknown-linux-gnu-0.15.10":
+    "e3e9e5c791542f00d95edc74a506e1ac24efc0af9574de01ab338187bf1ff9f6",
+  "x86_64-unknown-linux-musl-0.15.10":
+    "8b0a16bae81e371c9b6176a27fdb9db1deaa04c4cfe87e8604a898cc31686500",
+  "aarch64-apple-darwin-0.15.9":
+    "013d878f17c625550e4a6b19235c22fc229639f66f563bb72cb2c896aeca11e8",
+  "aarch64-pc-windows-msvc-0.15.9":
+    "813c3b9cf0c01ef913bfbc8d2dd17e140a8c3d54ae1b8f8c20ac53e2871674f0",
+  "aarch64-unknown-linux-gnu-0.15.9":
+    "ea71b14433318bed364e0dbb04203e57027cf134ab909d5e452be28d87d0fd08",
+  "aarch64-unknown-linux-musl-0.15.9":
+    "e017dd0c1fd7475aaddc49bde8cddcee3c27d42f6ce139a96df0c1022e06d85b",
+  "arm-unknown-linux-musleabihf-0.15.9":
+    "593382b4b5271cf63b8ea9972c7475a299f341ce8a9c22127ce1f8b7d82fcfe1",
+  "armv7-unknown-linux-gnueabihf-0.15.9":
+    "3c12ad897c62954fdc6a5c0f7baddd06f1cb37f1987618fa243ebd00a7b67d86",
+  "armv7-unknown-linux-musleabihf-0.15.9":
+    "9d9ebfe0075c7a6411f771ba79e210a3dffc4ba9706b542c5db72dc39d922893",
+  "i686-pc-windows-msvc-0.15.9":
+    "46cdcacb4522e19a26a18d586abb6addc68b4254bea958e93a347d7566add1c3",
+  "i686-unknown-linux-gnu-0.15.9":
+    "c04ddaa542d36b0483e325d29b00520242cf6b4e78e4cea0b73f0c74c77459ef",
+  "i686-unknown-linux-musl-0.15.9":
+    "97145060b15819b7d31df7c3fd160b02397e89c40069d485915ce6fbe92cb769",
+  "powerpc64le-unknown-linux-gnu-0.15.9":
+    "56e522a316427281d590aff0bcece176aedb15e9329799c1ada5cd8fd5e17b71",
+  "riscv64gc-unknown-linux-gnu-0.15.9":
+    "e0499cfd557515133118cc4dafb65a805c9656833a66b2fddaee9a9f8e847de4",
+  "s390x-unknown-linux-gnu-0.15.9":
+    "7402b9bdb1aaa79387f5b702696ec75d9ebed26f0a8e5097fc58924418c92097",
+  "x86_64-apple-darwin-0.15.9":
+    "7e0fe9daba25848f85cb3d43e47ecd7d23f14e92e8799f92c1bcd8319a4ce4f8",
+  "x86_64-pc-windows-msvc-0.15.9":
+    "e38fddd19805bc8f7329003c2abdaf49d8ca9e5bc0c6702e8472e16f127bcd44",
+  "x86_64-unknown-linux-gnu-0.15.9":
+    "223ce40fbea2245b0a650abf9f5093a6009b56a04e5e63c036f446cab328dcf7",
+  "x86_64-unknown-linux-musl-0.15.9":
+    "e30e6e50dbf925b42335f28e2fa296d404294f294159b314dca47b88317fc477",
+  "aarch64-apple-darwin-0.15.8":
+    "94fc061f928c8f2b04c4b3a98aad2b1b04f38b4c808839bc5b33a2f0a63a47a3",
+  "aarch64-pc-windows-msvc-0.15.8":
+    "5e2941bff2f14fa9b48532bba67d1bbeec2c26d5fecc5a4bc0f76d813ad644dc",
+  "aarch64-unknown-linux-gnu-0.15.8":
+    "7df2a2c86f1017936d8ce7b74d451ed05f2c648af8cf89add7ac0e4f3635f386",
+  "aarch64-unknown-linux-musl-0.15.8":
+    "15e6a6c21696bbe59c56d0f1c437452b960bcdfe81ecc3bc19fa89e6a7d70eb6",
+  "arm-unknown-linux-musleabihf-0.15.8":
+    "49847e5d218aa17da9be67df543d7c635e67558356e67406f97db0742776ed6b",
+  "armv7-unknown-linux-gnueabihf-0.15.8":
+    "4116ec65accfc2463a30720407f239339f72b1e40a66b341a9450651f3b43976",
+  "armv7-unknown-linux-musleabihf-0.15.8":
+    "e35ad1094bc8ef40b4d60fd32dbc6b129c4d9d4283f7ac3c838189f614c81d83",
+  "i686-pc-windows-msvc-0.15.8":
+    "01fd5224726810986121e1618602f2c24332a6abd2476d37c73d695be36679a7",
+  "i686-unknown-linux-gnu-0.15.8":
+    "66bf0839b384700624d946390ceb4493a787b5e56b93dd17795e2d5111db01f7",
+  "i686-unknown-linux-musl-0.15.8":
+    "098040cc3fdcb01efffbefa83bad0ccf4ecbcc00b7d0b5489f405d633fad1d5a",
+  "powerpc64le-unknown-linux-gnu-0.15.8":
+    "b3664a2793b002ef65888eb2818d449ede3d34b16ee71f17e8f1851b3d22eb23",
+  "riscv64gc-unknown-linux-gnu-0.15.8":
+    "7557039907a61cd7f1c7bad06fd77bdc38a7b2436471fe0b58e662d78ae13964",
+  "s390x-unknown-linux-gnu-0.15.8":
+    "127a53b418e6828816e156bf7ae959f70394ed67882bf9d69bcd15f3b34c6eba",
+  "x86_64-apple-darwin-0.15.8":
+    "153d1801068df606290e832058ce2e5601584ac302788a055d0390adf6c772ce",
+  "x86_64-pc-windows-msvc-0.15.8":
+    "1e6ebd021dc9cefa8b9f15b5d6500c275ec49a0f2da968824845c34f30060c78",
+  "x86_64-unknown-linux-gnu-0.15.8":
+    "45a6ed01c5b32873d4f6239f5fd6d9adde782295261b4a65962d754b3e37a849",
+  "x86_64-unknown-linux-musl-0.15.8":
+    "d541beae99d550ed4abb3a1d026b907886c7cdf44a533b24624871e3d8c81330",
+  "aarch64-apple-darwin-0.15.7":
+    "e573cdb504fce521af501cc16b7018fb6560ac0e7af5d05056c942b3a1ad5a79",
+  "aarch64-pc-windows-msvc-0.15.7":
+    "beb2eb063e52f197694fb79045cef276735a7becbbd8f8f79e1c99613a12d7e7",
+  "aarch64-unknown-linux-gnu-0.15.7":
+    "aee72470734c4220d367b269c3e901b7134485ecc70fe8635ff8141f09d9d11f",
+  "aarch64-unknown-linux-musl-0.15.7":
+    "a6e07403e1a2287ba87676e1e9fd3c6f392d2042ed4eb0ca83cda9d549926bfa",
+  "arm-unknown-linux-musleabihf-0.15.7":
+    "d5f527f70067a4cfaa7218383781ee5e0a5dcc0bbe9122c4fa8f6d1a88a991f8",
+  "armv7-unknown-linux-gnueabihf-0.15.7":
+    "0daac568f418577bc5e31c6c5d53f590c99dc42b740310a627ba0dc99dfcfe66",
+  "armv7-unknown-linux-musleabihf-0.15.7":
+    "9fbc574fcc28e104d0da617ab2655c904185f990660029483897aa76d2e60cea",
+  "i686-pc-windows-msvc-0.15.7":
+    "d6e02b3f65c29c64f443d7f0ebeb3a5a08b12fccfb3325d7ba2e026dedd2855b",
+  "i686-unknown-linux-gnu-0.15.7":
+    "18aa2cb27a5e383574189bf1983c9fdb9b1c6b9c1331f90cf03a5b0032c8325b",
+  "i686-unknown-linux-musl-0.15.7":
+    "02b6f4a2f6abf35e8e657e579e91718fbb36cf75e8f3095f13908d3d33dc4e66",
+  "powerpc64le-unknown-linux-gnu-0.15.7":
+    "ab153c03e331accb127098a8467e415524d8b2035a277f250e0b50908588bcf4",
+  "riscv64gc-unknown-linux-gnu-0.15.7":
+    "cf71700aed80851a8d32cd663e00d22b6a3eb03e17e057e0a63c7aaff4f20c57",
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+  "x86_64-unknown-linux-gnu-0.15.0":
+    "b38e69fb31501ebee3aba8e1778547bb2557adaf6b8f9dfae6f05980ee68b8ed",
+  "x86_64-unknown-linux-musl-0.15.0":
+    "f2bd69f091517ebc49405319a6e7818b1037e250b8d539336aa0b91c44ffa4aa",
  "aarch64-apple-darwin-0.14.14":
    "76a9b0ebe57d0eee56940dbe0b62462578d1369cca8314ed0d2a6f2102292d4f",
  "aarch64-pc-windows-msvc-0.14.14":
@@ -2,16 +2,16 @@ import { promises as fs } from "node:fs";
 import * as path from "node:path";
 import * as core from "@actions/core";
 import * as tc from "@actions/tool-cache";
-import { Octokit } from "@octokit/core";
-import { paginateRest } from "@octokit/plugin-paginate-rest";
-import { restEndpointMethods } from "@octokit/plugin-rest-endpoint-methods";
-import * as pep440 from "@renovatebot/pep440";
 import * as semver from "semver";
-import { OWNER, REPO, TOOL_CACHE_NAME } from "../utils/constants";
+import {
+  ASTRAL_MIRROR_PREFIX,
+  GITHUB_RELEASES_PREFIX,
+  TOOL_CACHE_NAME,
+  VERSIONS_MANIFEST_URL,
+} from "../utils/constants";
 import type { Architecture, Platform } from "../utils/platforms";
 import { validateChecksum } from "./checksum/checksum";
-
-const PaginatingOctokit = Octokit.plugin(paginateRest, restEndpointMethods);
+import { getArtifact } from "./manifest";

 export function tryGetFromToolCache(
  arch: Architecture,
@@ -32,31 +32,46 @@ export async function downloadVersion(
  platform: Platform,
  arch: Architecture,
  version: string,
-  checkSum: string | undefined,
+  checksum: string | undefined,
  githubToken: string,
+  manifestUrl?: string,
 ): Promise<{ version: string; cachedToolDir: string }> {
-  const artifact = `ruff-${arch}-${platform}`;
-  let extension = ".tar.gz";
-  if (platform === "pc-windows-msvc") {
-    extension = ".zip";
-  }
-  const downloadUrl = constructDownloadUrl(version, platform, arch);
-  core.debug(`Downloading ruff from "${downloadUrl}" ...`);
+  const artifact = await getArtifact(version, arch, platform, manifestUrl);

-  const downloadPath = await tc.downloadTool(
-    downloadUrl,
-    undefined,
-    githubToken,
+  if (!artifact) {
+    throw new Error(
+      getMissingArtifactMessage(version, arch, platform, manifestUrl),
+    );
+  }
+
+  // For the default astral-sh/versions source, checksum validation relies on
+  // user input or the built-in KNOWN_CHECKSUMS table, not manifest sha256 values.
+  const resolvedChecksum =
+    manifestUrl === undefined
+      ? checksum
+      : resolveChecksum(checksum, artifact.checksum);
+
+  const downloadPath = await downloadArtifact(
+    artifact.downloadUrl,
+    platform,
+    arch,
+    version,
+    getDownloadToken(artifact.downloadUrl, githubToken),
+  );
+  await validateChecksum(
+    resolvedChecksum,
+    downloadPath,
+    arch,
+    platform,
+    version,
  );
-  core.debug(`Downloaded ruff to "${downloadPath}"`);
-  await validateChecksum(checkSum, downloadPath, arch, platform, version);

  const extractedDir = await extractDownloadedArtifact(
    version,
    downloadPath,
-    extension,
+    getExtension(platform),
    platform,
-    artifact,
+    `ruff-${arch}-${platform}`,
  );

  const cachedToolDir = await tc.cacheDir(
@@ -65,25 +80,60 @@ export async function downloadVersion(
    version,
    arch,
  );
-  return { cachedToolDir, version: version };
+  return { cachedToolDir, version };
 }

-function constructDownloadUrl(
-  version: string,
+export function rewriteToMirror(url: string): string | undefined {
+  if (!url.startsWith(GITHUB_RELEASES_PREFIX)) {
+    return undefined;
+  }
+
+  return ASTRAL_MIRROR_PREFIX + url.slice(GITHUB_RELEASES_PREFIX.length);
+}
+
+async function downloadArtifact(
+  downloadUrl: string,
  platform: Platform,
  arch: Architecture,
-): string {
-  const artifactVersionSuffix =
-    semver.lte(version, "v0.4.10") && semver.gte(version, "v0.1.8")
-      ? `-${version}`
-      : "";
-  const artifact = `ruff${artifactVersionSuffix}-${arch}-${platform}`;
-  let extension = ".tar.gz";
-  if (platform === "pc-windows-msvc") {
-    extension = ".zip";
+  version: string,
+  githubToken: string | undefined,
+): Promise<string> {
+  const mirrorUrl = rewriteToMirror(downloadUrl);
+  const resolvedDownloadUrl = mirrorUrl ?? downloadUrl;
+
+  try {
+    return await downloadFile(
+      resolvedDownloadUrl,
+      mirrorUrl !== undefined ? undefined : githubToken,
+    );
+  } catch (err) {
+    if (mirrorUrl === undefined) {
+      throw err;
+    }
+
+    core.warning(
+      `Failed to download from mirror, falling back to GitHub Releases: ${(err as Error).message}`,
+    );
+
+    return await downloadFile(
+      constructDownloadUrl(version, platform, arch),
+      githubToken,
+    );
  }
-  const versionPrefix = semver.lte(version, "v0.4.10") ? "v" : "";
-  return `https://github.com/${OWNER}/${REPO}/releases/download/${versionPrefix}${version}/${artifact}${extension}`;
+}
+
+async function downloadFile(
+  downloadUrl: string,
+  githubToken: string | undefined,
+): Promise<string> {
+  core.info(`Downloading ruff from "${downloadUrl}" ...`);
+  const downloadPath = await tc.downloadTool(
+    downloadUrl,
+    undefined,
+    githubToken,
+  );
+  core.debug(`Downloaded ruff to "${downloadPath}"`);
+  return downloadPath;
 }

 async function extractDownloadedArtifact(
@@ -98,7 +148,7 @@ async function extractDownloadedArtifact(
    const fullPathWithExtension = `${downloadPath}${extension}`;
    await fs.copyFile(downloadPath, fullPathWithExtension);
    ruffDir = await tc.extractZip(fullPathWithExtension);
-    // On windows extracting the zip does not create an intermediate directory
+    // On windows extracting the zip does not create an intermediate directory.
  } else {
    ruffDir = await tc.extractTar(downloadPath);
    if (semver.gte(version, "v0.5.0")) {
@@ -111,116 +161,57 @@ async function extractDownloadedArtifact(
  return ruffDir;
 }

-export async function resolveVersion(
-  versionInput: string,
-  githubToken: string,
-): Promise<string> {
-  core.debug(`Resolving ${versionInput}...`);
-  const version =
-    versionInput === "latest"
-      ? await getLatestVersion(githubToken)
-      : versionInput;
-  if (tc.isExplicitVersion(version)) {
-    core.debug(`Version ${version} is an explicit version.`);
-    return version;
-  }
-  const availableVersions = await getAvailableVersions(githubToken);
-  const resolvedVersion = maxSatisfying(availableVersions, version);
-  if (resolvedVersion === undefined) {
-    throw new Error(`No version found for ${version}`);
-  }
-  core.debug(`Resolved version: ${resolvedVersion}`);
-  return resolvedVersion;
-}
-
-async function getAvailableVersions(githubToken: string): Promise<string[]> {
-  try {
-    const octokit = new PaginatingOctokit({
-      auth: githubToken,
-    });
-    return await getReleaseTagNames(octokit);
-  } catch (err) {
-    if ((err as Error).message.includes("Bad credentials")) {
-      core.info(
-        "No (valid) GitHub token provided. Falling back to anonymous. Requests might be rate limited.",
-      );
-      const octokit = new PaginatingOctokit();
-      return await getReleaseTagNames(octokit);
-    }
-    throw err;
-  }
-}
-
-async function getReleaseTagNames(
-  octokit: InstanceType<typeof PaginatingOctokit>,
-): Promise<string[]> {
-  const response = await octokit.paginate(octokit.rest.repos.listReleases, {
-    owner: OWNER,
-    repo: REPO,
-  });
-  const releaseTagNames = response.map((release) => release.tag_name);
-  if (releaseTagNames.length === 0) {
-    throw Error(
-      "Github API request failed while getting releases. Check the GitHub status page for outages. Try again later.",
-    );
-  }
-  return response.map((release) => release.tag_name);
-}
-
-async function getLatestVersion(githubToken: string) {
-  const octokit = new PaginatingOctokit({
-    auth: githubToken,
-  });
-
-  let latestRelease: { tag_name: string } | undefined;
-  try {
-    latestRelease = await getLatestRelease(octokit);
-  } catch (err) {
-    if ((err as Error).message.includes("Bad credentials")) {
-      core.info(
-        "No (valid) GitHub token provided. Falling back to anonymous. Requests might be rate limited.",
-      );
-      const octokit = new PaginatingOctokit();
-      latestRelease = await getLatestRelease(octokit);
-    } else {
-      core.error(
-        "Github API request failed while getting latest release. Check the GitHub status page for outages. Try again later.",
-      );
-      throw err;
-    }
-  }
-
-  if (!latestRelease) {
-    throw new Error("Could not determine latest release.");
-  }
-  return latestRelease.tag_name;
-}
-
-async function getLatestRelease(
-  octokit: InstanceType<typeof PaginatingOctokit>,
-) {
-  const { data: latestRelease } = await octokit.rest.repos.getLatestRelease({
-    owner: OWNER,
-    repo: REPO,
-  });
-  return latestRelease;
-}
-
-function maxSatisfying(
-  versions: string[],
+function getMissingArtifactMessage(
  version: string,
-): string | undefined {
-  const maxSemver = tc.evaluateVersions(versions, version);
-  if (maxSemver !== "") {
-    core.debug(`Found a version that satisfies the semver range: ${maxSemver}`);
-    return maxSemver;
+  arch: Architecture,
+  platform: Platform,
+  manifestUrl?: string,
+): string {
+  if (manifestUrl === undefined) {
+    return `Could not find artifact for version ${version}, arch ${arch}, platform ${platform} in ${VERSIONS_MANIFEST_URL} .`;
  }
-  const maxPep440 = pep440.maxSatisfying(versions, version);
-  if (maxPep440 !== null) {
-    core.debug(
-      `Found a version that satisfies the pep440 specifier: ${maxPep440}`,
-    );
-    return maxPep440;
-  }
-  return undefined;
+
+  return `manifest-file does not contain version ${version}, arch ${arch}, platform ${platform}.`;
+}
+
+function resolveChecksum(
+  checksum: string | undefined,
+  manifestChecksum: string,
+): string {
+  return checksum !== undefined && checksum !== ""
+    ? checksum
+    : manifestChecksum;
+}
+
+function getDownloadToken(
+  downloadUrl: string,
+  githubToken: string,
+): string | undefined {
+  return downloadUrl.startsWith(GITHUB_RELEASES_PREFIX)
+    ? githubToken
+    : undefined;
+}
+
+function constructDownloadUrl(
+  version: string,
+  platform: Platform,
+  arch: Architecture,
+): string {
+  const normalizedVersion = stripVersionPrefix(version);
+  const artifactVersionSuffix =
+    semver.lte(version, "v0.4.10") && semver.gte(version, "v0.1.8")
+      ? `-${normalizedVersion}`
+      : "";
+  const artifact = `ruff${artifactVersionSuffix}-${arch}-${platform}`;
+  const versionPrefix = semver.lte(version, "v0.4.10") ? "v" : "";
+
+  return `${GITHUB_RELEASES_PREFIX}${versionPrefix}${normalizedVersion}/${artifact}${getExtension(platform)}`;
+}
+
+function stripVersionPrefix(version: string): string {
+  return version.startsWith("v") ? version.slice(1) : version;
+}
+
+function getExtension(platform: Platform): string {
+  return platform === "pc-windows-msvc" ? ".zip" : ".tar.gz";
 }
@@ -0,0 +1,243 @@
+import * as core from "@actions/core";
+import { VERSIONS_MANIFEST_URL } from "../utils/constants";
+import { fetch } from "../utils/fetch";
+import { selectDefaultVariant } from "./variant-selection";
+
+export interface ManifestArtifact {
+  platform: string;
+  variant?: string;
+  url: string;
+  archive_format: string;
+  sha256: string;
+}
+
+export interface ManifestVersion {
+  version: string;
+  artifacts: ManifestArtifact[];
+}
+
+export interface ArtifactResult {
+  archiveFormat: string;
+  checksum: string;
+  downloadUrl: string;
+}
+
+const cachedManifestData = new Map<string, ManifestVersion[]>();
+
+export async function fetchManifest(
+  manifestUrl: string = VERSIONS_MANIFEST_URL,
+): Promise<ManifestVersion[]> {
+  const cachedVersions = cachedManifestData.get(manifestUrl);
+  if (cachedVersions !== undefined) {
+    core.debug(`Using cached manifest data from ${manifestUrl}`);
+    return cachedVersions;
+  }
+
+  core.info(`Fetching manifest data from ${manifestUrl} ...`);
+  const response = await fetch(manifestUrl, {});
+  if (!response.ok) {
+    throw new Error(
+      `Failed to fetch manifest data: ${response.status} ${response.statusText}`,
+    );
+  }
+
+  const body = await response.text();
+  const versions = parseManifest(body, manifestUrl);
+  cachedManifestData.set(manifestUrl, versions);
+  return versions;
+}
+
+export function parseManifest(
+  data: string,
+  sourceDescription: string,
+): ManifestVersion[] {
+  const trimmed = data.trim();
+  if (trimmed === "") {
+    throw new Error(`Manifest at ${sourceDescription} is empty.`);
+  }
+
+  if (trimmed.startsWith("[")) {
+    throw new Error(
+      `Legacy JSON array manifests are no longer supported in ${sourceDescription}. Use the astral-sh/versions manifest format instead.`,
+    );
+  }
+
+  const versions: ManifestVersion[] = [];
+
+  for (const [index, line] of data.split("\n").entries()) {
+    const record = line.trim();
+    if (record === "") {
+      continue;
+    }
+
+    let parsed: unknown;
+    try {
+      parsed = JSON.parse(record);
+    } catch (error) {
+      throw new Error(
+        `Failed to parse manifest data from ${sourceDescription} at line ${index + 1}: ${(error as Error).message}`,
+      );
+    }
+
+    if (!isManifestVersion(parsed)) {
+      throw new Error(
+        `Invalid manifest record in ${sourceDescription} at line ${index + 1}.`,
+      );
+    }
+
+    versions.push(parsed);
+  }
+
+  if (versions.length === 0) {
+    throw new Error(`No manifest data found in ${sourceDescription}.`);
+  }
+
+  return versions;
+}
+
+export async function getLatestVersion(
+  manifestUrl: string = VERSIONS_MANIFEST_URL,
+): Promise<string> {
+  const latestVersion = (await fetchManifest(manifestUrl))[0]?.version;
+
+  if (latestVersion === undefined) {
+    throw new Error("No versions found in manifest data");
+  }
+
+  core.debug(`Latest version from manifest: ${latestVersion}`);
+  return latestVersion;
+}
+
+export async function getAllVersions(
+  manifestUrl: string = VERSIONS_MANIFEST_URL,
+): Promise<string[]> {
+  core.info(
+    `Getting available versions from ${manifestSource(manifestUrl)} ...`,
+  );
+  const versions = await fetchManifest(manifestUrl);
+  return versions.map((versionData) => versionData.version);
+}
+
+export async function getArtifact(
+  version: string,
+  arch: string,
+  platform: string,
+  manifestUrl: string = VERSIONS_MANIFEST_URL,
+): Promise<ArtifactResult | undefined> {
+  const versions = await fetchManifest(manifestUrl);
+  const versionData = versions.find((candidate) =>
+    matchesManifestVersion(candidate.version, version),
+  );
+  if (!versionData) {
+    core.debug(`Version ${version} not found in manifest ${manifestUrl}`);
+    return undefined;
+  }
+
+  const targetPlatforms = getTargetPlatforms(
+    versionData.version,
+    arch,
+    platform,
+  );
+  const matchingArtifacts = versionData.artifacts.filter((candidate) =>
+    targetPlatforms.includes(candidate.platform),
+  );
+
+  if (matchingArtifacts.length === 0) {
+    core.debug(
+      `Artifact for ${targetPlatforms.join(" or ")} not found in version ${version}. Available platforms: ${versionData.artifacts
+        .map((candidate) => candidate.platform)
+        .join(", ")}`,
+    );
+    return undefined;
+  }
+
+  const artifact = selectDefaultVariant(
+    matchingArtifacts,
+    `Multiple artifacts found for ${targetPlatforms.join(" or ")} in version ${version}`,
+  );
+
+  return {
+    archiveFormat: artifact.archive_format,
+    checksum: artifact.sha256,
+    downloadUrl: artifact.url,
+  };
+}
+
+export function clearManifestCache(manifestUrl?: string): void {
+  if (manifestUrl === undefined) {
+    cachedManifestData.clear();
+    return;
+  }
+
+  cachedManifestData.delete(manifestUrl);
+}
+
+function manifestSource(manifestUrl: string): string {
+  if (manifestUrl === VERSIONS_MANIFEST_URL) {
+    return VERSIONS_MANIFEST_URL;
+  }
+
+  return `manifest-file ${manifestUrl}`;
+}
+
+function matchesManifestVersion(
+  manifestVersion: string,
+  requestedVersion: string,
+): boolean {
+  return (
+    manifestVersion === requestedVersion ||
+    manifestVersion === withVersionPrefix(requestedVersion)
+  );
+}
+
+function getTargetPlatforms(
+  manifestVersion: string,
+  arch: string,
+  platform: string,
+): string[] {
+  const targetPlatform = `${arch}-${platform}`;
+  const versionPrefixedTargetPlatform = `${stripVersionPrefix(manifestVersion)}-${targetPlatform}`;
+
+  return [targetPlatform, versionPrefixedTargetPlatform];
+}
+
+function withVersionPrefix(version: string): string {
+  return version.startsWith("v") ? version : `v${version}`;
+}
+
+function stripVersionPrefix(version: string): string {
+  return version.startsWith("v") ? version.slice(1) : version;
+}
+
+function isManifestVersion(value: unknown): value is ManifestVersion {
+  if (!isRecord(value)) {
+    return false;
+  }
+
+  if (typeof value.version !== "string" || !Array.isArray(value.artifacts)) {
+    return false;
+  }
+
+  return value.artifacts.every(isManifestArtifact);
+}
+
+function isManifestArtifact(value: unknown): value is ManifestArtifact {
+  if (!isRecord(value)) {
+    return false;
+  }
+
+  const variantIsValid =
+    typeof value.variant === "string" || value.variant === undefined;
+
+  return (
+    typeof value.archive_format === "string" &&
+    typeof value.platform === "string" &&
+    typeof value.sha256 === "string" &&
+    typeof value.url === "string" &&
+    variantIsValid
+  );
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null;
+}
@@ -0,0 +1,39 @@
+interface VariantAwareEntry {
+  variant?: string;
+}
+
+export function selectDefaultVariant<T extends VariantAwareEntry>(
+  entries: T[],
+  duplicateEntryDescription: string,
+): T {
+  const firstEntry = entries[0];
+  if (firstEntry === undefined) {
+    throw new Error("selectDefaultVariant requires at least one candidate.");
+  }
+
+  if (entries.length === 1) {
+    return firstEntry;
+  }
+
+  const defaultEntries = entries.filter((entry) =>
+    isDefaultVariant(entry.variant),
+  );
+  if (defaultEntries.length === 1) {
+    return defaultEntries[0];
+  }
+
+  throw new Error(
+    `${duplicateEntryDescription} with variants ${formatVariants(entries)}. ruff-action currently requires a single default variant for duplicate platform entries.`,
+  );
+}
+
+function isDefaultVariant(variant: string | undefined): boolean {
+  return variant === undefined || variant === "default";
+}
+
+function formatVariants<T extends VariantAwareEntry>(entries: T[]): string {
+  return entries
+    .map((entry) => entry.variant ?? "default")
+    .sort((left, right) => left.localeCompare(right))
+    .join(", ");
+}
@@ -4,13 +4,13 @@ import * as exec from "@actions/exec";
 import * as semver from "semver";
 import {
  downloadVersion,
-  resolveVersion,
  tryGetFromToolCache,
 } from "./download/download-version";
 import {
  args,
  checkSum,
  githubToken,
+  manifestFile,
  src,
  version,
  versionFile as versionFileInput,
@@ -21,8 +21,7 @@ import {
  getPlatform,
  type Platform,
 } from "./utils/platforms";
-import { getRuffVersionFromRequirementsFile } from "./utils/pyproject";
-import { findPyprojectToml } from "./utils/pyproject-finder";
+import { resolveRuffVersion } from "./version/resolve";

 async function run(): Promise<void> {
  const platform = getPlatform();
@@ -62,6 +61,7 @@ async function setupRuff(
  githubToken: string,
 ): Promise<{ ruffDir: string; version: string }> {
  const resolvedVersion = await determineVersion();
+  const manifestUrl = manifestFile || undefined;
  if (semver.lt(resolvedVersion, "v0.0.247")) {
    throw Error(
      "This action does not support ruff versions older than 0.0.247",
@@ -82,6 +82,7 @@ async function setupRuff(
    resolvedVersion,
    checkSum,
    githubToken,
+    manifestUrl,
  );

  return {
@@ -91,38 +92,13 @@ async function setupRuff(
 }

 async function determineVersion(): Promise<string> {
-  if (versionFileInput !== "" && version !== "") {
-    throw Error("It is not allowed to specify both version and version-file");
-  }
-  if (version !== "") {
-    return await resolveVersion(version, githubToken);
-  }
-  if (versionFileInput !== "") {
-    const versionFromPyproject =
-      getRuffVersionFromRequirementsFile(versionFileInput);
-    if (versionFromPyproject === undefined) {
-      core.warning(
-        `Could not parse version from ${versionFileInput}. Using latest version.`,
-      );
-    }
-    return await resolveVersion(versionFromPyproject || "latest", githubToken);
-  }
-  const pyProjectPath = findPyprojectToml(
-    src,
-    process.env.GITHUB_WORKSPACE || ".",
-  );
-  if (!pyProjectPath) {
-    core.info(`Could not find pyproject.toml. Using latest version.`);
-    return await resolveVersion("latest", githubToken);
-  }
-  const versionFromPyproject =
-    getRuffVersionFromRequirementsFile(pyProjectPath);
-  if (versionFromPyproject === undefined) {
-    core.info(
-      `Could not parse version from ${pyProjectPath}. Using latest version.`,
-    );
-  }
-  return await resolveVersion(versionFromPyproject || "latest", githubToken);
+  return await resolveRuffVersion({
+    manifestFile: manifestFile || undefined,
+    sourceDirectory: src,
+    version,
+    versionFile: versionFileInput,
+    workspaceRoot: process.env.GITHUB_WORKSPACE || ".",
+  });
 }

 function addRuffToPath(cachedPath: string): void {
@@ -136,16 +112,17 @@ function setOutputFormat() {
 }

 function addMatchers(): void {
-  const matchersPath = path.join(
-    __dirname,
-    `..${path.sep}..`,
-    ".github",
-    "matchers",
-  );
+  const actionRoot = getActionRoot();
+  const matchersPath = path.join(actionRoot, ".github", "matchers");
  core.info(`##[add-matcher]${path.join(matchersPath, "check.json")}`);
  core.info(`##[add-matcher]${path.join(matchersPath, "format.json")}`);
 }

+function getActionRoot(): string {
+  const entrypoint = process.argv[1] ?? process.cwd();
+  return path.resolve(path.dirname(entrypoint), "..", "..");
+}
+
 async function runRuff(
  ruffExecutablePath: string,
  args: string[],
@@ -10,9 +10,9 @@ const PaginatingOctokit = Octokit.plugin(paginateRest, restEndpointMethods);

 async function run(): Promise<void> {
  const checksumFilePath = process.argv.slice(2)[0];
-  const github_token = process.argv.slice(2)[1];
+  const githubToken = process.argv.slice(2)[1];

-  const octokit = new PaginatingOctokit({ auth: github_token });
+  const octokit = new PaginatingOctokit({ auth: githubToken });

  const response = await octokit.paginate(octokit.rest.repos.listReleases, {
    owner: OWNER,
@@ -1,3 +1,9 @@
 export const REPO = "ruff";
 export const OWNER = "astral-sh";
 export const TOOL_CACHE_NAME = "ruff";
+export const VERSIONS_MANIFEST_URL =
+  "https://raw.githubusercontent.com/astral-sh/versions/main/v1/ruff.ndjson";
+export const GITHUB_RELEASES_PREFIX =
+  "https://github.com/astral-sh/ruff/releases/download/";
+export const ASTRAL_MIRROR_PREFIX =
+  "https://releases.astral.sh/github/ruff/releases/download/";
@@ -0,0 +1,21 @@
+import { ProxyAgent, type RequestInit, fetch as undiciFetch } from "undici";
+
+export function getProxyAgent() {
+  const httpProxy = process.env.HTTP_PROXY || process.env.http_proxy;
+  if (httpProxy) {
+    return new ProxyAgent(httpProxy);
+  }
+
+  const httpsProxy = process.env.HTTPS_PROXY || process.env.https_proxy;
+  if (httpsProxy) {
+    return new ProxyAgent(httpsProxy);
+  }
+
+  return undefined;
+}
+
+export const fetch = async (url: string, opts: RequestInit) =>
+  await undiciFetch(url, {
+    dispatcher: getProxyAgent(),
+    ...opts,
+  });
@@ -6,3 +6,4 @@ export const githubToken = core.getInput("github-token");
 export const args = core.getInput("args");
 export const src = core.getInput("src");
 export const versionFile = core.getInput("version-file");
+export const manifestFile = core.getInput("manifest-file");
@@ -1,183 +0,0 @@
-import * as path from "node:path";
-import * as core from "@actions/core";
-import { findPyprojectToml } from "./pyproject-finder";
-
-jest.mock("@actions/core", () => ({
-  debug: jest.fn(),
-  info: jest.fn(),
-}));
-
-describe("findPyprojectToml", () => {
-  beforeEach(() => {
-    jest.clearAllMocks();
-  });
-
-  describe("when pyproject.toml exists in src directory", () => {
-    it("should return the exact path", () => {
-      const fixturesDir = path.join(
-        __dirname,
-        "..",
-        "..",
-        "__tests__",
-        "fixtures",
-      );
-      const workspaceRoot = path.join(__dirname, "..", "..");
-
-      const result = findPyprojectToml(fixturesDir, workspaceRoot);
-
-      expect(result).toContain("pyproject.toml");
-      expect(result).toContain("fixtures");
-      expect(core.info).toHaveBeenCalled();
-    });
-  });
-
-  describe("when pyproject.toml exists only in parent directory", () => {
-    it("should search upwards and find the parent's pyproject.toml", () => {
-      // subproject doesn't have a pyproject.toml, but its parent (parent-config-project) does
-      const subprojectDir = path.join(
-        __dirname,
-        "..",
-        "..",
-        "__tests__",
-        "fixtures",
-        "parent-config-project",
-        "subproject",
-      );
-      const workspaceRoot = path.join(__dirname, "..", "..");
-
-      const result = findPyprojectToml(subprojectDir, workspaceRoot);
-
-      expect(result).toBeTruthy();
-      expect(result).toContain("pyproject.toml");
-      expect(result).toContain("parent-config-project");
-      expect(core.info).toHaveBeenCalled();
-    });
-  });
-
-  describe("boundary conditions", () => {
-    it("should stop searching at workspace root and return undefined when not found", () => {
-      // Create a path that won't have pyproject.toml above it
-      const nodeModulesDir = path.join(
-        __dirname,
-        "..",
-        "..",
-        "node_modules",
-        "@actions",
-      );
-      const workspaceRoot = path.join(__dirname, "..", "..");
-
-      const result = findPyprojectToml(nodeModulesDir, workspaceRoot);
-
-      // Should return undefined since there's no pyproject.toml in the search path
-      expect(result).toBeUndefined();
-      expect(core.info).not.toHaveBeenCalledWith(
-        expect.stringContaining("Found pyproject.toml"),
-      );
-    });
-
-    it("should find pyproject.toml when it exists at workspace root", () => {
-      // Use parent-config-project as the "workspace root" for this test
-      // Start from subproject (which has no pyproject.toml) to search up to workspace root
-      const subprojectDir = path.join(
-        __dirname,
-        "..",
-        "..",
-        "__tests__",
-        "fixtures",
-        "parent-config-project",
-        "subproject",
-      );
-      const workspaceRoot = path.join(
-        __dirname,
-        "..",
-        "..",
-        "__tests__",
-        "fixtures",
-        "parent-config-project",
-      );
-
-      const result = findPyprojectToml(subprojectDir, workspaceRoot);
-
-      expect(result).toBeTruthy();
-      expect(result).toContain("pyproject.toml");
-      expect(result).toContain("parent-config-project");
-    });
-
-    it("should stop at workspace root even if searching from it", () => {
-      const workspaceRoot = path.join(
-        __dirname,
-        "..",
-        "..",
-        "__tests__",
-        "fixtures",
-      );
-
-      const result = findPyprojectToml(workspaceRoot, workspaceRoot);
-
-      // Should find pyproject.toml at workspace root
-      expect(result).toBeTruthy();
-      expect(result).toContain("pyproject.toml");
-      expect(result).toContain("fixtures");
-    });
-  });
-
-  describe("edge cases", () => {
-    it("should handle relative paths", () => {
-      const srcDir = "./__tests__/fixtures";
-      const workspaceRoot = ".";
-
-      const result = findPyprojectToml(srcDir, workspaceRoot);
-
-      // Should work with relative paths
-      expect(result).toBeTruthy();
-      expect(result).toContain("pyproject.toml");
-    });
-
-    it("should handle when src equals workspace root", () => {
-      const workspaceRoot = path.join(
-        __dirname,
-        "..",
-        "..",
-        "__tests__",
-        "fixtures",
-      );
-      const result = findPyprojectToml(workspaceRoot, workspaceRoot);
-
-      expect(result).toBeTruthy();
-      expect(result).toContain("pyproject.toml");
-      expect(result).toContain("fixtures");
-    });
-
-    it("should log debug messages for each checked path", () => {
-      const pythonProjectDir = path.join(
-        __dirname,
-        "..",
-        "..",
-        "__tests__",
-        "fixtures",
-        "python-project",
-      );
-      const workspaceRoot = path.join(__dirname, "..", "..");
-
-      findPyprojectToml(pythonProjectDir, workspaceRoot);
-
-      expect(core.debug).toHaveBeenCalled();
-      const debugCalls = (core.debug as jest.Mock).mock.calls;
-      expect(debugCalls.length).toBeGreaterThan(0);
-
-      // First debug call should be for the starting directory
-      expect(debugCalls[0][0]).toContain("Checking for");
-      expect(debugCalls[0][0]).toContain("python-project");
-    });
-
-    it("should handle paths with trailing slashes", () => {
-      const fixturesDir = `${path.join(__dirname, "..", "..", "__tests__", "fixtures")}/`;
-      const workspaceRoot = path.join(__dirname, "..", "..");
-
-      const result = findPyprojectToml(fixturesDir, workspaceRoot);
-
-      expect(result).toBeTruthy();
-      expect(result).toContain("pyproject.toml");
-    });
-  });
-});
@@ -26,30 +26,20 @@ export function findPyprojectToml(
      core.info(`Found pyproject.toml at ${pyprojectPath}`);
      return pyprojectPath;
    }
-
-    // Check if we've reached the workspace root
    if (currentDir === resolvedWorkspaceRoot) {
-      // If we're at workspace root and didn't find it, stop searching
-      break;
+      return undefined;
    }

-    // Move up to parent directory
    const parentDir = path.dirname(currentDir);
-
-    // If parent is the same as current, we've reached the filesystem root
-    if (parentDir === currentDir) {
-      break;
+    if (
+      parentDir === currentDir ||
+      !isPathWithinWorkspace(parentDir, resolvedWorkspaceRoot)
+    ) {
+      return undefined;
    }

    currentDir = parentDir;
-
-    // If we've gone past the workspace root, stop searching
-    if (isPathWithinWorkspace(currentDir, resolvedWorkspaceRoot) === false) {
-      break;
-    }
  }
-
-  return undefined;
 }

 /**
@@ -62,18 +52,7 @@ export function findPyprojectToml(
 function isPathWithinWorkspace(
  checkPath: string,
  workspaceRoot: string,
-): boolean | undefined {
-  try {
-    const checkPathResolved = path.resolve(checkPath);
-    const workspaceRootResolved = path.resolve(workspaceRoot);
-
-    // Check if checkPath starts with workspaceRoot (case-insensitive on Windows)
-    const relativePath = path.relative(
-      workspaceRootResolved,
-      checkPathResolved,
-    );
-    return !relativePath.startsWith("..") && !path.isAbsolute(relativePath);
-  } catch {
-    return undefined;
-  }
+): boolean {
+  const relativePath = path.relative(workspaceRoot, checkPath);
+  return !relativePath.startsWith("..") && !path.isAbsolute(relativePath);
 }
@@ -1,188 +0,0 @@
-import * as core from "@actions/core";
-import { findRuffVersionInSpec } from "./pyproject";
-
-jest.mock("@actions/core", () => ({
-  info: jest.fn(),
-  warning: jest.fn(),
-}));
-
-describe("findRuffVersionInSpec", () => {
-  beforeEach(() => {
-    jest.clearAllMocks();
-  });
-
-  describe("ruff dependency strings", () => {
-    it("should extract version from 'ruff==0.9.3'", () => {
-      const result = findRuffVersionInSpec("ruff==0.9.3");
-      expect(result).toBe("0.9.3");
-      expect(core.info).toHaveBeenCalledWith(
-        "Found ruff version in requirements file: 0.9.3",
-      );
-      expect(core.warning).not.toHaveBeenCalled();
-    });
-
-    it("should extract version from 'ruff>=0.14'", () => {
-      const result = findRuffVersionInSpec("ruff>=0.14");
-      expect(result).toBe(">=0.14");
-      expect(core.warning).not.toHaveBeenCalled();
-    });
-
-    it("should extract version from 'ruff ~=1.0.0'", () => {
-      const result = findRuffVersionInSpec("ruff ~=1.0.0");
-      expect(result).toBe("~=1.0.0");
-      expect(core.warning).not.toHaveBeenCalled();
-    });
-
-    it("should extract version from 'ruff>=0.14,<1.0'", () => {
-      const result = findRuffVersionInSpec("ruff>=0.14,<1.0");
-      expect(result).toBe(">=0.14,<1.0");
-      expect(core.warning).not.toHaveBeenCalled();
-    });
-
-    it("should extract version from 'ruff>=0.14,<2.0,!=1.5.0'", () => {
-      const result = findRuffVersionInSpec("ruff>=0.14,<2.0,!=1.5.0");
-      expect(result).toBe(">=0.14,<2.0,!=1.5.0");
-      expect(core.warning).not.toHaveBeenCalled();
-    });
-
-    it("should return undefined for non-ruff dependency 'another-dep 0.1.6'", () => {
-      const result = findRuffVersionInSpec("another-dep 0.1.6");
-      expect(result).toBeUndefined();
-      expect(core.info).not.toHaveBeenCalled();
-      expect(core.warning).not.toHaveBeenCalled();
-    });
-
-    it("should return undefined for non-ruff dependency 'another-dep==0.1.6'", () => {
-      const result = findRuffVersionInSpec("another-dep==0.1.6");
-      expect(result).toBeUndefined();
-      expect(core.info).not.toHaveBeenCalled();
-      expect(core.warning).not.toHaveBeenCalled();
-    });
-
-    it("should strip trailing backslash", () => {
-      const result = findRuffVersionInSpec("ruff==0.9.3 \\");
-      expect(result).toBe("0.9.3");
-      expect(core.info).toHaveBeenCalledWith(
-        "Found ruff version in requirements file: 0.9.3",
-      );
-      expect(core.warning).not.toHaveBeenCalled();
-    });
-
-    it("should strip trailing backslash with whitespace", () => {
-      const result = findRuffVersionInSpec("  ruff==0.9.3  \\  ");
-      expect(result).toBe("0.9.3");
-      expect(core.warning).not.toHaveBeenCalled();
-    });
-  });
-
-  describe("environment markers", () => {
-    it("should strip python_version environment marker", () => {
-      const result = findRuffVersionInSpec(
-        'ruff>=0.14 ; python_version >= "3.11"',
-      );
-      expect(result).toBe(">=0.14");
-      expect(core.info).toHaveBeenCalledWith(
-        "Found ruff version in requirements file: >=0.14",
-      );
-      expect(core.warning).toHaveBeenCalledWith(
-        "Environment markers are ignored. ruff is a standalone tool that works independently of Python version.",
-      );
-    });
-
-    it("should strip sys_platform environment marker", () => {
-      const result = findRuffVersionInSpec(
-        "ruff==0.9.3 ; sys_platform == 'linux'",
-      );
-      expect(result).toBe("0.9.3");
-      expect(core.warning).toHaveBeenCalledWith(
-        "Environment markers are ignored. ruff is a standalone tool that works independently of Python version.",
-      );
-    });
-
-    it("should strip multiple environment markers", () => {
-      const result = findRuffVersionInSpec(
-        'ruff>=0.14 ; python_version >= "3.11" and sys_platform == "linux"',
-      );
-      expect(result).toBe(">=0.14");
-      expect(core.warning).toHaveBeenCalledWith(
-        "Environment markers are ignored. ruff is a standalone tool that works independently of Python version.",
-      );
-    });
-
-    it("should handle environment markers with multiple constraints", () => {
-      const result = findRuffVersionInSpec(
-        'ruff>=0.14,<1.0 ; python_version >= "3.11"',
-      );
-      expect(result).toBe(">=0.14,<1.0");
-      expect(core.warning).toHaveBeenCalledWith(
-        "Environment markers are ignored. ruff is a standalone tool that works independently of Python version.",
-      );
-    });
-  });
-
-  describe("edge cases", () => {
-    it("should handle whitespace", () => {
-      const result = findRuffVersionInSpec("  ruff  >=0.14  ");
-      expect(result).toBe(">=0.14");
-      expect(core.warning).not.toHaveBeenCalled();
-    });
-
-    it("should handle whitespace with environment markers", () => {
-      const result = findRuffVersionInSpec(
-        "  ruff  >=0.14  ;  python_version >= '3.11'  ",
-      );
-      expect(result).toBe(">=0.14");
-      expect(core.warning).toHaveBeenCalled();
-    });
-
-    it("should return undefined for empty string", () => {
-      const result = findRuffVersionInSpec("");
-      expect(result).toBeUndefined();
-      expect(core.info).not.toHaveBeenCalled();
-      expect(core.warning).not.toHaveBeenCalled();
-    });
-
-    it("should return undefined for whitespace only", () => {
-      const result = findRuffVersionInSpec("   ");
-      expect(result).toBeUndefined();
-      expect(core.info).not.toHaveBeenCalled();
-      expect(core.warning).not.toHaveBeenCalled();
-    });
-
-    it("should return undefined for just semicolon", () => {
-      const result = findRuffVersionInSpec(";");
-      expect(result).toBeUndefined();
-      expect(core.info).not.toHaveBeenCalled();
-      expect(core.warning).not.toHaveBeenCalled();
-    });
-
-    it("should handle exact example from issue #256", () => {
-      const result = findRuffVersionInSpec(
-        'ruff>=0.14 ; python_version >= "3.11"',
-      );
-      expect(result).toBe(">=0.14");
-      expect(core.info).toHaveBeenCalledWith(
-        "Found ruff version in requirements file: >=0.14",
-      );
-      expect(core.warning).toHaveBeenCalledWith(
-        "Environment markers are ignored. ruff is a standalone tool that works independently of Python version.",
-      );
-    });
-
-    it("should handle single-quoted environment markers", () => {
-      const result = findRuffVersionInSpec(
-        "ruff>=0.14 ; python_version >= '3.11'",
-      );
-      expect(result).toBe(">=0.14");
-      expect(core.warning).toHaveBeenCalled();
-    });
-
-    it("should handle double-quoted environment markers", () => {
-      const result = findRuffVersionInSpec(
-        'ruff>=0.14 ; python_version >= "3.11"',
-      );
-      expect(result).toBe(">=0.14");
-      expect(core.warning).toHaveBeenCalled();
-    });
-  });
-});
@@ -1,130 +0,0 @@
-import * as fs from "node:fs";
-import * as core from "@actions/core";
-import * as toml from "smol-toml";
-
-/**
- * Find ruff version in a dependency specification.
- * Only handles strings that start with "ruff" (e.g., "ruff==0.9.3").
- * Returns undefined for non-ruff dependencies.
- * Strips environment markers (everything after ';').
- * Strips leading '==' from exact version specifiers (PEP 440) for downstream compatibility.
- *
- * @internal This is exported for testing purposes only.
- */
-export function findRuffVersionInSpec(spec: string): string | undefined {
-  const trimmedSpec = spec.trim();
-
-  const fullDepMatch = trimmedSpec.match(/^ruff\s*(.+)$/);
-  let versionSpec: string;
-  if (fullDepMatch) {
-    versionSpec = fullDepMatch[1];
-  } else {
-    return undefined;
-  }
-
-  // Strip trailing backslash (line continuation)
-  versionSpec = versionSpec.replace(/\\$/, "").trim();
-
-  // Strip environment markers (everything after ';')
-  const match = versionSpec.match(/^([^;]+)(?:;.*)?$/);
-
-  if (match) {
-    let version = match[1].trim();
-    if (version) {
-      // Strip leading '==' from exact version specifiers for compatibility with semver
-      if (version.startsWith("==")) {
-        version = version.slice(2);
-      }
-      if (trimmedSpec.includes(";")) {
-        core.warning(
-          "Environment markers are ignored. ruff is a standalone tool that works independently of Python version.",
-        );
-      }
-      core.info(`Found ruff version in requirements file: ${version}`);
-      return version;
-    }
-  }
-
-  return undefined;
-}
-
-function getRuffVersionFromAllDependencies(
-  allDependencies: string[],
-): string | undefined {
-  return allDependencies
-    .map((dep) => findRuffVersionInSpec(dep))
-    .find((version) => version !== undefined);
-}
-
-interface Pyproject {
-  project?: {
-    dependencies?: string[];
-    "optional-dependencies"?: Record<string, string[]>;
-  };
-  "dependency-groups"?: Record<string, Array<string | object>>;
-  tool?: {
-    poetry?: {
-      dependencies?: Record<string, string | object>;
-      group?: Record<string, { dependencies: Record<string, string | object> }>;
-    };
-  };
-}
-
-function parsePyproject(pyprojectContent: string): string | undefined {
-  const pyproject: Pyproject = toml.parse(pyprojectContent);
-  const dependencies: string[] = pyproject?.project?.dependencies || [];
-  const optionalDependencies: string[] = Object.values(
-    pyproject?.project?.["optional-dependencies"] || {},
-  ).flat();
-  const devDependencies: string[] = Object.values(
-    pyproject?.["dependency-groups"] || {},
-  )
-    .flat()
-    .filter((item: string | object) => typeof item === "string");
-  return (
-    getRuffVersionFromAllDependencies(
-      dependencies.concat(optionalDependencies, devDependencies),
-    ) || getRuffVersionFromPoetryGroups(pyproject)
-  );
-}
-
-function getRuffVersionFromPoetryGroups(
-  pyproject: Pyproject,
-): string | undefined {
-  // Special handling for Poetry until it supports PEP 735
-  // See: <https://github.com/python-poetry/poetry/issues/9751>
-  const poetry = pyproject?.tool?.poetry || {};
-  const poetryGroups = Object.values(poetry.group || {});
-  if (poetry.dependencies) {
-    poetryGroups.unshift({ dependencies: poetry.dependencies });
-  }
-  return poetryGroups
-    .flatMap((group) => Object.entries(group.dependencies))
-    .map(([name, spec]) => {
-      if (typeof spec === "string") {
-        return findRuffVersionInSpec(`${name} ${spec}`);
-      }
-      return undefined;
-    })
-    .find((version) => version !== undefined);
-}
-
-export function getRuffVersionFromRequirementsFile(
-  filePath: string,
-): string | undefined {
-  if (!fs.existsSync(filePath)) {
-    core.warning(`Could not find file: ${filePath}`);
-    return undefined;
-  }
-  const pyprojectContent = fs.readFileSync(filePath, "utf-8");
-  if (filePath.endsWith(".txt")) {
-    return getRuffVersionFromAllDependencies(pyprojectContent.split("\n"));
-  }
-  try {
-    return parsePyproject(pyprojectContent);
-  } catch (err) {
-    const message = (err as Error).message;
-    core.warning(`Error while parsing ${filePath}: ${message}`);
-    return undefined;
-  }
-}
@@ -0,0 +1,185 @@
+import fs from "node:fs";
+import * as core from "@actions/core";
+import * as toml from "smol-toml";
+import { normalizeVersionSpecifier } from "./specifier";
+import type { ParsedVersionFile, VersionFileFormat } from "./types";
+
+interface VersionFileParser {
+  format: VersionFileFormat;
+  parse(filePath: string): string | undefined;
+  supports(filePath: string): boolean;
+}
+
+interface Pyproject {
+  project?: {
+    dependencies?: string[];
+    "optional-dependencies"?: Record<string, string[]>;
+  };
+  "dependency-groups"?: Record<string, Array<string | object>>;
+  tool?: {
+    poetry?: {
+      dependencies?: Record<string, string | object>;
+      group?: Record<string, { dependencies: Record<string, string | object> }>;
+    };
+  };
+}
+
+const VERSION_FILE_PARSERS: VersionFileParser[] = [
+  {
+    format: "pyproject.toml",
+    parse: (filePath) => {
+      const fileContent = fs.readFileSync(filePath, "utf-8");
+      return getRuffVersionFromPyprojectContent(fileContent);
+    },
+    supports: (filePath) => filePath.endsWith("pyproject.toml"),
+  },
+  {
+    format: "requirements",
+    parse: (filePath) => {
+      const fileContent = fs.readFileSync(filePath, "utf-8");
+      return getRuffVersionFromRequirementsText(fileContent);
+    },
+    supports: (filePath) => filePath.endsWith(".txt"),
+  },
+];
+
+export function getParsedVersionFile(
+  filePath: string,
+): ParsedVersionFile | undefined {
+  core.info(`Trying to find version for ruff in: ${filePath}`);
+
+  if (!fs.existsSync(filePath)) {
+    core.warning(`Could not find file: ${filePath}`);
+    return undefined;
+  }
+
+  const parser = getVersionFileParser(filePath);
+  if (parser === undefined) {
+    return undefined;
+  }
+
+  try {
+    const specifier = parser.parse(filePath);
+    if (specifier === undefined) {
+      return undefined;
+    }
+
+    const normalizedSpecifier = normalizeVersionSpecifier(specifier);
+    core.info(`Found version for ruff in ${filePath}: ${normalizedSpecifier}`);
+    return {
+      format: parser.format,
+      specifier: normalizedSpecifier,
+    };
+  } catch (error) {
+    core.warning(
+      `Error while parsing ${filePath}: ${(error as Error).message}`,
+    );
+    return undefined;
+  }
+}
+
+export function getRuffVersionFromFile(filePath: string): string | undefined {
+  return getParsedVersionFile(filePath)?.specifier;
+}
+
+export function findRuffVersionInSpec(spec: string): string | undefined {
+  const trimmedSpec = spec.trim();
+
+  if (!trimmedSpec.startsWith("ruff")) {
+    return undefined;
+  }
+
+  let versionSpec = trimmedSpec.slice("ruff".length);
+  if (!versionSpec.match(/^(?:\s+|[=<>~!])/)) {
+    return undefined;
+  }
+
+  versionSpec = versionSpec.replace(/\\$/, "").trim();
+
+  const match = versionSpec.match(/^([^;]+)(?:;.*)?$/);
+
+  if (match) {
+    let version = match[1].trim();
+    if (version) {
+      version = normalizeVersionSpecifier(version);
+      if (trimmedSpec.includes(";")) {
+        core.warning(
+          "Environment markers are ignored. ruff is a standalone tool that works independently of Python version.",
+        );
+      }
+      core.info(`Found ruff version in requirements file: ${version}`);
+      return version;
+    }
+  }
+
+  return undefined;
+}
+
+export function getRuffVersionFromRequirementsText(
+  fileContent: string,
+): string | undefined {
+  return getRuffVersionFromAllDependencies(fileContent.split("\n"));
+}
+
+export function getRuffVersionFromPyprojectContent(
+  pyprojectContent: string,
+): string | undefined {
+  const pyproject = parsePyprojectContent(pyprojectContent);
+  return getRuffVersionFromParsedPyproject(pyproject);
+}
+
+export function parsePyprojectContent(pyprojectContent: string): Pyproject {
+  return toml.parse(pyprojectContent) as Pyproject;
+}
+
+function getVersionFileParser(filePath: string): VersionFileParser | undefined {
+  return VERSION_FILE_PARSERS.find((parser) => parser.supports(filePath));
+}
+
+function getRuffVersionFromParsedPyproject(
+  pyproject: Pyproject,
+): string | undefined {
+  const dependencies: string[] = pyproject.project?.dependencies || [];
+  const optionalDependencies: string[] = Object.values(
+    pyproject.project?.["optional-dependencies"] || {},
+  ).flat();
+  const devDependencies: string[] = Object.values(
+    pyproject["dependency-groups"] || {},
+  )
+    .flat()
+    .filter((item: string | object) => typeof item === "string");
+
+  return (
+    getRuffVersionFromAllDependencies(
+      dependencies.concat(optionalDependencies, devDependencies),
+    ) || getRuffVersionFromPoetryGroups(pyproject)
+  );
+}
+
+function getRuffVersionFromPoetryGroups(
+  pyproject: Pyproject,
+): string | undefined {
+  const poetry = pyproject.tool?.poetry || {};
+  const poetryGroups = Object.values(poetry.group || {});
+  if (poetry.dependencies) {
+    poetryGroups.unshift({ dependencies: poetry.dependencies });
+  }
+
+  return poetryGroups
+    .flatMap((group) => Object.entries(group.dependencies))
+    .map(([name, spec]) => {
+      if (typeof spec === "string") {
+        return findRuffVersionInSpec(`${name} ${spec}`);
+      }
+      return undefined;
+    })
+    .find((version) => version !== undefined);
+}
+
+function getRuffVersionFromAllDependencies(
+  allDependencies: string[],
+): string | undefined {
+  return allDependencies
+    .map((dependency) => findRuffVersionInSpec(dependency))
+    .find((version) => version !== undefined);
+}
@@ -0,0 +1,125 @@
+import * as core from "@actions/core";
+import * as tc from "@actions/tool-cache";
+import * as pep440 from "@renovatebot/pep440";
+import { getAllVersions, getLatestVersion } from "../download/manifest";
+import {
+  type ParsedVersionSpecifier,
+  parseVersionSpecifier,
+} from "./specifier";
+import type { ResolveRuffVersionOptions } from "./types";
+import { resolveVersionRequest } from "./version-request-resolver";
+
+interface ConcreteVersionResolutionContext {
+  manifestUrl?: string;
+  parsedSpecifier: ParsedVersionSpecifier;
+}
+
+interface ConcreteVersionResolver {
+  resolve(
+    context: ConcreteVersionResolutionContext,
+  ): Promise<string | undefined>;
+}
+
+class ExactVersionResolver implements ConcreteVersionResolver {
+  async resolve(
+    context: ConcreteVersionResolutionContext,
+  ): Promise<string | undefined> {
+    if (context.parsedSpecifier.kind !== "exact") {
+      return undefined;
+    }
+
+    core.debug(
+      `Version ${context.parsedSpecifier.normalized} is an explicit version.`,
+    );
+    return context.parsedSpecifier.normalized;
+  }
+}
+
+class LatestVersionResolver implements ConcreteVersionResolver {
+  async resolve(
+    context: ConcreteVersionResolutionContext,
+  ): Promise<string | undefined> {
+    if (context.parsedSpecifier.kind !== "latest") {
+      return undefined;
+    }
+
+    return await getLatestVersion(context.manifestUrl);
+  }
+}
+
+class RangeVersionResolver implements ConcreteVersionResolver {
+  async resolve(
+    context: ConcreteVersionResolutionContext,
+  ): Promise<string | undefined> {
+    if (context.parsedSpecifier.kind !== "range") {
+      return undefined;
+    }
+
+    const availableVersions = await getAllVersions(context.manifestUrl);
+    const resolvedVersion = maxSatisfying(
+      availableVersions,
+      context.parsedSpecifier.normalized,
+    );
+    if (resolvedVersion === undefined) {
+      throw new Error(`No version found for ${context.parsedSpecifier.raw}`);
+    }
+
+    core.debug(`Resolved version: ${resolvedVersion}`);
+    return resolvedVersion;
+  }
+}
+
+const CONCRETE_VERSION_RESOLVERS: ConcreteVersionResolver[] = [
+  new ExactVersionResolver(),
+  new LatestVersionResolver(),
+  new RangeVersionResolver(),
+];
+
+export async function resolveRuffVersion(
+  options: ResolveRuffVersionOptions,
+): Promise<string> {
+  const request = resolveVersionRequest(options);
+  return await resolveVersion(request.specifier, options.manifestFile);
+}
+
+export async function resolveVersion(
+  versionInput: string,
+  manifestUrl?: string,
+): Promise<string> {
+  core.debug(`Resolving ${versionInput}...`);
+
+  const context: ConcreteVersionResolutionContext = {
+    manifestUrl,
+    parsedSpecifier: parseVersionSpecifier(versionInput),
+  };
+
+  for (const resolver of CONCRETE_VERSION_RESOLVERS) {
+    const version = await resolver.resolve(context);
+    if (version !== undefined) {
+      return version;
+    }
+  }
+
+  throw new Error(`No version found for ${versionInput}`);
+}
+
+function maxSatisfying(
+  versions: string[],
+  version: string,
+): string | undefined {
+  const maxSemver = tc.evaluateVersions(versions, version);
+  if (maxSemver !== "") {
+    core.debug(`Found a version that satisfies the semver range: ${maxSemver}`);
+    return maxSemver;
+  }
+
+  const maxPep440 = pep440.maxSatisfying(versions, version);
+  if (maxPep440 !== null) {
+    core.debug(
+      `Found a version that satisfies the pep440 specifier: ${maxPep440}`,
+    );
+    return maxPep440;
+  }
+
+  return undefined;
+}
@@ -0,0 +1,57 @@
+import * as tc from "@actions/tool-cache";
+
+export type ParsedVersionSpecifier =
+  | {
+      kind: "exact";
+      normalized: string;
+      raw: string;
+    }
+  | {
+      kind: "latest";
+      normalized: "latest";
+      raw: string;
+    }
+  | {
+      kind: "range";
+      normalized: string;
+      raw: string;
+    };
+
+export function normalizeVersionSpecifier(specifier: string): string {
+  const trimmedSpecifier = specifier.trim();
+
+  if (trimmedSpecifier.startsWith("==")) {
+    return trimmedSpecifier.slice(2);
+  }
+
+  return trimmedSpecifier;
+}
+
+export function parseVersionSpecifier(
+  specifier: string,
+): ParsedVersionSpecifier {
+  const raw = specifier.trim();
+  const normalized = normalizeVersionSpecifier(raw);
+
+  if (normalized === "latest") {
+    return {
+      kind: "latest",
+      normalized: "latest",
+      raw,
+    };
+  }
+
+  if (tc.isExplicitVersion(normalized)) {
+    return {
+      kind: "exact",
+      normalized,
+      raw,
+    };
+  }
+
+  return {
+    kind: "range",
+    normalized,
+    raw,
+  };
+}
@@ -0,0 +1,27 @@
+export type VersionSource =
+  | "input"
+  | "version-file"
+  | "pyproject.toml"
+  | "default";
+
+export type VersionFileFormat = "pyproject.toml" | "requirements";
+
+export interface ParsedVersionFile {
+  format: VersionFileFormat;
+  specifier: string;
+}
+
+export interface ResolveRuffVersionOptions {
+  manifestFile?: string;
+  sourceDirectory: string;
+  version?: string;
+  versionFile?: string;
+  workspaceRoot: string;
+}
+
+export interface VersionRequest {
+  format?: VersionFileFormat;
+  source: VersionSource;
+  sourcePath?: string;
+  specifier: string;
+}
@@ -0,0 +1,162 @@
+import * as core from "@actions/core";
+import { findPyprojectToml } from "../utils/pyproject-finder";
+import { getParsedVersionFile } from "./file-parser";
+import { normalizeVersionSpecifier } from "./specifier";
+import type {
+  ParsedVersionFile,
+  ResolveRuffVersionOptions,
+  VersionRequest,
+} from "./types";
+
+export interface VersionRequestResolver {
+  resolve(context: VersionRequestContext): VersionRequest | undefined;
+}
+
+export class VersionRequestContext {
+  readonly sourceDirectory: string;
+  readonly version: string | undefined;
+  readonly versionFile: string | undefined;
+  readonly workspaceRoot: string;
+
+  private readonly parsedFiles = new Map<
+    string,
+    ParsedVersionFile | undefined
+  >();
+
+  constructor(
+    version: string | undefined,
+    versionFile: string | undefined,
+    sourceDirectory: string,
+    workspaceRoot: string,
+  ) {
+    this.version = version;
+    this.versionFile = versionFile;
+    this.sourceDirectory = sourceDirectory;
+    this.workspaceRoot = workspaceRoot;
+  }
+
+  getVersionFile(filePath: string): ParsedVersionFile | undefined {
+    const cachedResult = this.parsedFiles.get(filePath);
+    if (cachedResult !== undefined || this.parsedFiles.has(filePath)) {
+      return cachedResult;
+    }
+
+    const result = getParsedVersionFile(filePath);
+    this.parsedFiles.set(filePath, result);
+    return result;
+  }
+
+  getWorkspacePyprojectPath(): string | undefined {
+    return findPyprojectToml(this.sourceDirectory, this.workspaceRoot);
+  }
+}
+
+export class ExplicitInputVersionResolver implements VersionRequestResolver {
+  resolve(context: VersionRequestContext): VersionRequest | undefined {
+    if (context.version === undefined) {
+      return undefined;
+    }
+
+    return {
+      source: "input",
+      specifier: normalizeVersionSpecifier(context.version),
+    };
+  }
+}
+
+export class VersionFileVersionResolver implements VersionRequestResolver {
+  resolve(context: VersionRequestContext): VersionRequest | undefined {
+    if (context.versionFile === undefined) {
+      return undefined;
+    }
+
+    const versionFile = context.getVersionFile(context.versionFile);
+    if (versionFile === undefined) {
+      core.warning(
+        `Could not parse version from ${context.versionFile}. Using latest version.`,
+      );
+      return undefined;
+    }
+
+    return {
+      format: versionFile.format,
+      source: "version-file",
+      sourcePath: context.versionFile,
+      specifier: versionFile.specifier,
+    };
+  }
+}
+
+export class WorkspaceVersionResolver implements VersionRequestResolver {
+  resolve(context: VersionRequestContext): VersionRequest | undefined {
+    const pyprojectPath = context.getWorkspacePyprojectPath();
+    if (!pyprojectPath) {
+      core.info("Could not find pyproject.toml. Using latest version.");
+      return undefined;
+    }
+
+    const versionFile = context.getVersionFile(pyprojectPath);
+    if (versionFile === undefined) {
+      core.info(
+        `Could not parse version from ${pyprojectPath}. Using latest version.`,
+      );
+      return undefined;
+    }
+
+    return {
+      format: versionFile.format,
+      source: "pyproject.toml",
+      sourcePath: pyprojectPath,
+      specifier: versionFile.specifier,
+    };
+  }
+}
+
+export class LatestVersionResolver implements VersionRequestResolver {
+  resolve(): VersionRequest {
+    return {
+      source: "default",
+      specifier: "latest",
+    };
+  }
+}
+
+const VERSION_REQUEST_RESOLVERS: VersionRequestResolver[] = [
+  new ExplicitInputVersionResolver(),
+  new VersionFileVersionResolver(),
+  new WorkspaceVersionResolver(),
+  new LatestVersionResolver(),
+];
+
+export function resolveVersionRequest(
+  options: ResolveRuffVersionOptions,
+): VersionRequest {
+  const version = emptyToUndefined(options.version);
+  const versionFile = emptyToUndefined(options.versionFile);
+
+  if (version !== undefined && versionFile !== undefined) {
+    throw new Error(
+      "It is not allowed to specify both version and version-file",
+    );
+  }
+
+  const context = new VersionRequestContext(
+    version,
+    versionFile,
+    options.sourceDirectory,
+    options.workspaceRoot,
+  );
+
+  for (const resolver of VERSION_REQUEST_RESOLVERS) {
+    const request = resolver.resolve(context);
+    if (request !== undefined) {
+      return request;
+    }
+  }
+
+  throw new Error("Could not resolve a requested Ruff version.");
+}
+
+function emptyToUndefined(value: string | undefined): string | undefined {
+  return value === undefined || value === "" ? undefined : value;
+}
@@ -1,12 +1,12 @@
 {
  "compilerOptions": {
-    "esModuleInterop": true /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */,
-    "module": "commonjs" /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */,
-    "noImplicitAny": true /* Raise error on expressions and declarations with an implied 'any' type. */,
-    "outDir": "./lib" /* Redirect output structure to the directory. */,
-    "rootDir": "./src" /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */,
-    "strict": true /* Enable all strict type-checking options. */,
-    "target": "ES2022" /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
+    "esModuleInterop": true,
+    "isolatedModules": true,
+    "module": "esnext",
+    "moduleResolution": "bundler",
+    "noImplicitAny": true,
+    "strict": true,
+    "target": "ES2022"
  },
-  "exclude": ["node_modules", "**/*.test.ts"]
+  "include": ["src/**/*.ts"]
 }
				`@@ -0,0 +1 @@`
				`{"version":"0.15.10","artifacts":[{"platform":"x86_64-unknown-linux-gnu","variant":"default","url":"https://github.com/astral-sh/ruff/releases/download/0.15.10/ruff-x86_64-unknown-linux-gnu.tar.gz","archive_format":"tar.gz","sha256":"e3e9e5c791542f00d95edc74a506e1ac24efc0af9574de01ab338187bf1ff9f6"}]}`