pr-reviewer-mcp

An MCP server exposing AI-powered GitHub PR review as tools, adapted from codewarrior (a webhook-driven GitHub App) into an on-demand tool server.

Why this exists

The original app reviews automatically when a PR opens — event-driven. This version reviews when explicitly asked, by you or by an agent — tool-driven. Same review pipeline (LangChain + Gemini), different trigger model and a different auth model (PAT instead of GitHub App installation tokens, since there's a human in the loop at call time instead of a webhook).

Tools

Tool	Description
`list_open_prs`	List open PRs for a repo
`get_pr_diff`	Fetch the raw diff, no AI
`review_file`	AI review of a single file in a PR
`review_pr`	Full AI review: all files in parallel + synthesized summary
`post_review_comment`	Post a review as a PR comment

Setup

npm install
cp .env.example .env

Fill in .env:

GITHUB_TOKEN — fine-grained PAT with Pull requests (read/write) and Contents (read) permissions on the repos you want to review
GOOGLE_API_KEY — from Google AI Studio

Running locally

npm start

This starts the server on stdio. It won't print anything to stdout (that channel is reserved for the MCP protocol) — status logs go to stderr.

Connecting to CLI or VS Code

Add to your MCP config (claude_desktop_config.json or equivalent):

{
  "mcpServers": {
    "pr-reviewer": {
      "command": "node",
      "args": ["/absolute/path/to/pr-reviewer-mcp/src/index.js"],
      "env": {
        "GITHUB_TOKEN": "your-token-here",
        "GOOGLE_API_KEY": "your-key-here"
      }
    }
  }
}

Restart your IDE, then you can ask things like:

"Review PR #12 on srivastava-aryan/dsa-tracker"

and it will call review_pr, decide whether to post it, and call post_review_comment if you confirm.

What changed from the original app

Auth: github-auth.js now uses a personal access token via @octokit/rest directly, instead of @octokit/auth-app + installation tokens. No webhook server, no Express, no smee-client.
Trigger: no webhook listener. Review happens when a tool is called.
Logging: console.log → console.error in the review pipeline, since stdout is reserved for MCP protocol messages on stdio transport.
Everything else — prompts, parallel file review, synthesis step — is unchanged from the original reviewer.js and diff-fetcher.js.

Next steps worth exploring

Swap stdio transport for HTTP/SSE if you want to host this remotely instead of running it locally per-user
Add a list_recent_reviews tool backed by a small DB, so repeated reviews on the same PR don't re-run from scratch
Add resource support (server.resource) to expose PR diffs as browsable MCP resources rather than only tool outputs