Originally published at claudeguide.io/claude-code-pr-review-automation

Claude Code Pull Request Review Automation: Full Setup Guide (2026)

Claude Code can automatically review pull requests by fetching the diff, analyzing changed files, and posting structured comments — triggered on every PR open or update via GitHub Actions. A working setup takes under 20 minutes and costs roughly $0.02-$0.08 per review with Claude Haiku. This guide walks through the complete pipeline: the Actions workflow, prompt engineering for useful reviews, posting comments via the GitHub API, and controlling costs at scale.

---

Why Automate PR Reviews with Claude Code?

Manual code review is a bottleneck. In a study of engineering teams, 35% of developer time blocked on PRs was waiting for reviewer availability — not the actual review itself.

Claude Code PR automation delivers:

• Immediate first-pass feedback — catches obvious bugs, style issues, and missing tests before a human reviewer looks
• Consistent review standards — the same checklist applied to every PR, regardless of reviewer fatigue
• 24/7 coverage — reviews happen at merge time, not when a reviewer happens to be online
• Documented rationale — Claude's comments are explanatory, not just "change this"

Cost benchmark: 100 PRs/month with average 200-line diffs costs approximately $4-8/month using Claude Haiku.

---

Architecture Overview

PR opened/updated
      ↓
GitHub Actions triggered
      ↓
Fetch PR diff (GitHub API)
      ↓
Send diff + review prompt → Claude API
      ↓
Parse Claude's response
      ↓
Post as PR comment (GitHub API)

---

Step 1: The GitHub Actions Workflow

# .github/workflows/claude-pr-review.yml
name: Claude PR Review

on:
  pull_request:
    types: [opened, synchronize]
    paths-ignore:
      - "*.md"
      - "docs/**"

permissions:
  pull-requests: write
  contents: read

jobs:
  review:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Get PR diff
        id: diff
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        run: |
          gh pr diff ${{ github.event.pull_request.number }} \
            --patch 

---

## Step 3: Prompt Engineering for Useful Reviews

The default review prompt above covers the basics. Customize it for your codebase:

### Language-Specific Prompts

python

Detect language from diff and customize

if ".py" in diff:
language_rules = """
Additional Python-specific checks:
- Type hints on all function signatures
- No bare except: clauses
- f-strings instead of % formatting
- Docstrings on public functions
"""
elif ".ts" in diff or ".tsx" in diff:
language_rules = """
Additional TypeScript-specific checks:
- No any types without justification
- Proper async/await error handling
- React hooks rules compliance
- No console.log left in code
"""

### Severity Filtering

If you only want critical issues posted as blocking reviews:

python

Parse Claude's response for critical issues

if "🔴 Critical" in review_text:
# Post as a blocking review request
subprocess.run([
"gh", "pr", "review", pr_number,
"--request-changes",
"--body-file", output_path
])
else:
# Post as informational comment
subprocess.run([
"gh", "pr", "comment", pr_number,
"--body-file", output_path
])

---

## Step 4: Skip Conditions

Not every PR needs a full review. Add skip logic to control costs:

yaml

• name: Check if review needed
  id: check
  run: |
  CHANGED_FILES=$(gh pr view ${{ github.event.pull_request.number }} \
  --json files --jq '.files | length')

  Skip if only docs changed

  ONLY_DOCS=$(gh pr diff ${{ github.event.pull_request.number }} \
  --name-only | grep -v ".md$" | wc -l)

  if [ "$ONLY_DOCS" -eq "0" ]; then
  echo "skip=true"