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GitHub Action that Reviews Every PR

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A classic high-value automation: have Claude review every pull request and post its findings as a comment — running headless in CI. Here's the shape, with the guardrails that keep it safe.

What it does​

On each PR: check out the diff, ask Claude to review it for bugs/edge-cases/convention issues, and post a comment. Humans still decide; Claude just gives a fast first pass.

The workflow (sketch)​

name: Claude PR review
on: pull_request
permissions:
  contents: read
  pull-requests: write   # to comment — NOT write to code
jobs:
  review:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with: { fetch-depth: 0 }
      - name: Review the diff
        env:
          ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
        run: |
          git diff origin/${{ github.base_ref }}...HEAD > /tmp/diff.patch
          claude -p "Review this diff for correctness bugs, missing edge cases, and
          security issues. Report ONLY high-confidence findings as a Markdown
          checklist with file:line. Diff:" < /tmp/diff.patch > /tmp/review.md
      # then post /tmp/review.md as a PR comment (e.g. with the gh CLI or an action)

(Exact headless invocation may differ — see the docs. The principle is: feed the diff, capture Markdown, post it.)

The guardrails (read Hardening Autonomous Runs)​

:::warning Least privilege in CI

  • Comment only. Grant pull-requests: write, not contents: write — the bot shouldn't push code.
  • Scope the token; never expose deploy/secret access to a job that reads untrusted PR content.
  • Treat PR content as untrusted — it can carry prompt injection; don't let the job take consequential actions.
  • Cap cost — large diffs cost tokens; consider reviewing changed files only. :::

Make it useful, not noisy​

  • Ask for high-confidence findings only — a wall of nitpicks gets ignored.
  • Keep it as a first pass, with humans making the merge call.

Next​