diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 7686ec3..f17db8c 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -431,6 +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:
@@ -456,6 +481,7 @@ jobs:
       - test-failure
       - test-multiple-src
       - test-parent-directory-pyproject
+      - test-custom-manifest-file
     if: always()
     steps:
       - name: All tests passed
diff --git a/README.md b/README.md
index bbd0bd2..0d14262 100644
--- a/README.md
+++ b/README.md
@@ -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)                                                | `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
 
@@ -155,6 +160,19 @@ Currently `pyproject.toml` and `requirements.txt` are supported.
     version-file: "my-path/to/pyproject.toml-or-requirements.txt"
 ```
 
+#### 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 +189,11 @@ 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)
diff --git a/__tests__/download/custom-manifest.ndjson b/__tests__/download/custom-manifest.ndjson
new file mode 100644
index 0000000..abb2f05
--- /dev/null
+++ b/__tests__/download/custom-manifest.ndjson
@@ -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"}]}
diff --git a/__tests__/download/download-version.test.ts b/__tests__/download/download-version.test.ts
new file mode 100644
index 0000000..950224a
--- /dev/null
+++ b/__tests__/download/download-version.test.ts
@@ -0,0 +1,509 @@
+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", () => ({
+  promises: {
+    copyFile: mockCopyFile,
+    readdir: mockReaddir,
+  },
+}));
+
+const { downloadVersion, resolveVersion, rewriteToMirror } = await import(
+  "../../src/download/download-version"
+);
+
+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();
+    });
+  });
+});
diff --git a/__tests__/download/manifest.test.ts b/__tests__/download/manifest.test.ts
new file mode 100644
index 0000000..c9128d0
--- /dev/null
+++ b/__tests__/download/manifest.test.ts
@@ -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",
+      );
+    });
+  });
+});
diff --git a/action.yml b/action.yml
index a72f645..4e47051 100644
--- a/action.yml
+++ b/action.yml
@@ -20,10 +20,12 @@ inputs:
   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:
diff --git a/dist/ruff-action/index.cjs b/dist/ruff-action/index.cjs
index 790eebc..b9a859c 100644
Binary files a/dist/ruff-action/index.cjs and b/dist/ruff-action/index.cjs differ
diff --git a/package-lock.json b/package-lock.json
index 703e8bc..37e2ec1 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -16,7 +16,8 @@
         "@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": "^2.4.7",
diff --git a/package.json b/package.json
index 1368edf..3425847 100644
--- a/package.json
+++ b/package.json
@@ -35,7 +35,8 @@
     "@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": "^2.4.7",
diff --git a/src/download/download-version.ts b/src/download/download-version.ts
index ecd269d..283cef7 100644
--- a/src/download/download-version.ts
+++ b/src/download/download-version.ts
@@ -2,16 +2,17 @@ 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 { getAllVersions, getArtifact, getLatestVersion } from "./manifest";
 
 export function tryGetFromToolCache(
   arch: Architecture,
@@ -32,31 +33,46 @@ 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 +81,60 @@ 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 +149,7 @@ 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")) {
@@ -113,18 +164,21 @@ async function extractDownloadedArtifact(
 
 export async function resolveVersion(
   versionInput: string,
-  githubToken: string,
+  manifestUrl?: string,
 ): Promise<string> {
   core.debug(`Resolving ${versionInput}...`);
+
   const version =
     versionInput === "latest"
-      ? await getLatestVersion(githubToken)
+      ? await getLatestVersion(manifestUrl)
       : versionInput;
+
   if (tc.isExplicitVersion(version)) {
     core.debug(`Version ${version} is an explicit version.`);
     return version;
   }
-  const availableVersions = await getAvailableVersions(githubToken);
+
+  const availableVersions = await getAvailableVersions(manifestUrl);
   const resolvedVersion = maxSatisfying(availableVersions, version);
   if (resolvedVersion === undefined) {
     throw new Error(`No version found for ${version}`);
@@ -133,77 +187,63 @@ export async function resolveVersion(
   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 getAvailableVersions(manifestUrl?: string): Promise<string[]> {
+  return await getAllVersions(manifestUrl);
 }
 
-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.",
-    );
+function getMissingArtifactMessage(
+  version: string,
+  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} .`;
   }
-  return response.map((release) => release.tag_name);
+
+  return `manifest-file does not contain version ${version}, arch ${arch}, platform ${platform}.`;
 }
 
-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;
+function resolveChecksum(
+  checksum: string | undefined,
+  manifestChecksum: string,
+): string {
+  return checksum !== undefined && checksum !== ""
+    ? checksum
+    : manifestChecksum;
 }
 
-async function getLatestRelease(
-  octokit: InstanceType<typeof PaginatingOctokit>,
-) {
-  const { data: latestRelease } = await octokit.rest.repos.getLatestRelease({
-    owner: OWNER,
-    repo: REPO,
-  });
-  return latestRelease;
+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";
 }
 
 function maxSatisfying(
diff --git a/src/download/manifest.ts b/src/download/manifest.ts
new file mode 100644
index 0000000..e79569a
--- /dev/null
+++ b/src/download/manifest.ts
@@ -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;
+}
diff --git a/src/download/variant-selection.ts b/src/download/variant-selection.ts
new file mode 100644
index 0000000..622fee2
--- /dev/null
+++ b/src/download/variant-selection.ts
@@ -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(", ");
+}
diff --git a/src/ruff-action.ts b/src/ruff-action.ts
index 4e659d3..68d873a 100644
--- a/src/ruff-action.ts
+++ b/src/ruff-action.ts
@@ -11,6 +11,7 @@ import {
   args,
   checkSum,
   githubToken,
+  manifestFile,
   src,
   version,
   versionFile as versionFileInput,
@@ -62,6 +63,7 @@ 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 +84,7 @@ async function setupRuff(
     resolvedVersion,
     checkSum,
     githubToken,
+    manifestUrl,
   );
 
   return {
@@ -95,7 +98,7 @@ async function determineVersion(): Promise<string> {
     throw Error("It is not allowed to specify both version and version-file");
   }
   if (version !== "") {
-    return await resolveVersion(version, githubToken);
+    return await resolveVersion(version, manifestFile || undefined);
   }
   if (versionFileInput !== "") {
     const versionFromPyproject =
@@ -105,7 +108,10 @@ async function determineVersion(): Promise<string> {
         `Could not parse version from ${versionFileInput}. Using latest version.`,
       );
     }
-    return await resolveVersion(versionFromPyproject || "latest", githubToken);
+    return await resolveVersion(
+      versionFromPyproject || "latest",
+      manifestFile || undefined,
+    );
   }
   const pyProjectPath = findPyprojectToml(
     src,
@@ -113,7 +119,7 @@ async function determineVersion(): Promise<string> {
   );
   if (!pyProjectPath) {
     core.info(`Could not find pyproject.toml. Using latest version.`);
-    return await resolveVersion("latest", githubToken);
+    return await resolveVersion("latest", manifestFile || undefined);
   }
   const versionFromPyproject =
     getRuffVersionFromRequirementsFile(pyProjectPath);
@@ -122,7 +128,10 @@ async function determineVersion(): Promise<string> {
       `Could not parse version from ${pyProjectPath}. Using latest version.`,
     );
   }
-  return await resolveVersion(versionFromPyproject || "latest", githubToken);
+  return await resolveVersion(
+    versionFromPyproject || "latest",
+    manifestFile || undefined,
+  );
 }
 
 function addRuffToPath(cachedPath: string): void {
diff --git a/src/utils/constants.ts b/src/utils/constants.ts
index 35e0414..bf0f794 100644
--- a/src/utils/constants.ts
+++ b/src/utils/constants.ts
@@ -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/";
diff --git a/src/utils/fetch.ts b/src/utils/fetch.ts
new file mode 100644
index 0000000..0830dfd
--- /dev/null
+++ b/src/utils/fetch.ts
@@ -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,
+  });
diff --git a/src/utils/inputs.ts b/src/utils/inputs.ts
index 6b59b93..ec4c1fa 100644
--- a/src/utils/inputs.ts
+++ b/src/utils/inputs.ts
@@ -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");