AI PR Review Skill

Automated pull request review using OpenRouter free models.

How It Works

1. GitHub Action triggers on every PR open or sync
2. Gets the PR diff via gh pr diff (truncated at 8000 chars)
3. Sends to OpenRouter (primary: Gemma 3 27B Free, fallback: Mistral 7B Free) for analysis
4. Posts structured review as PR comment (Summary / Issues / Suggestions)

Models

Both models are free-tier on OpenRouter. If both are unavailable, the workflow exits with a clear error message.

Setup

Requirements

• OPENROUTER_API_KEY in ~/.claude/secrets/secrets.env
• GH_TOKEN or GITHUB_TOKEN with PR write permissions
• gh CLI installed

GitHub Action Setup

Add .github/workflows/ai-review.yml to your repo (also available in this plugin repo):

name: AI Code Review
on:
  pull_request:
    types: [opened, synchronize]
jobs:
  review:
    runs-on: ubuntu-latest
    permissions:
      pull-requests: write
    steps:
      - uses: actions/checkout@v4

      - name: Validate API key
        run: |
          if [ -z "$OPENROUTER_API_KEY" ]; then
            echo "::error::OPENROUTER_API_KEY secret is not set."
            exit 1
          fi
        env:
          OPENROUTER_API_KEY: ${{ secrets.OPENROUTER_API_KEY }}

      - name: Get PR diff
        id: diff
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        run: |
          PR_DIFF=$(gh pr diff ${{ github.event.pull_request.number }} 2>/dev/null || echo "")
          if [ -z "$PR_DIFF" ]; then
            echo "skip=true" >> "$GITHUB_OUTPUT"
            exit 0
          fi
          PR_DIFF_TRUNCATED="${PR_DIFF:0:8000}"
          { echo "diff<<EOF_DIFF"; echo "$PR_DIFF_TRUNCATED"; echo "EOF_DIFF"; } >> "$GITHUB_OUTPUT"
          echo "skip=false" >> "$GITHUB_OUTPUT"

      - name: AI Review via OpenRouter
        if: steps.diff.outputs.skip == 'false'
        env:
          OPENROUTER_API_KEY: ${{ secrets.OPENROUTER_API_KEY }}
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          PR_DIFF: ${{ steps.diff.outputs.diff }}
          PR_NUMBER: ${{ github.event.pull_request.number }}
          PR_TITLE: ${{ github.event.pull_request.title }}
        run: |
          PRIMARY_MODEL="google/gemma-3-27b-it:free"
          FALLBACK_MODEL="mistralai/mistral-7b-instruct:free"

          PROMPT="Review PR #${PR_NUMBER}: ${PR_TITLE}\n\nDiff:\n${PR_DIFF}\n\nProvide:\n## Summary\n## Issues\n## Suggestions"

          for MODEL in "$PRIMARY_MODEL" "$FALLBACK_MODEL"; do
            PAYLOAD=$(python3 -c "
          import json,sys
          print(json.dumps({'model':'$MODEL','messages':[{'role':'user','content':sys.stdin.read()}],'max_tokens':1024}))" <<< "$PROMPT")
            RESPONSE=$(curl -s -w "\n%{http_code}" \
              -X POST https://openrouter.ai/api/v1/chat/completions \
              -H "Authorization: Bearer $OPENROUTER_API_KEY" \
              -H "Content-Type: application/json" \
              -d "$PAYLOAD")
            HTTP_CODE=$(echo "$RESPONSE" | tail -n1)
            BODY=$(echo "$RESPONSE" | head -n -1)
            if [ "$HTTP_CODE" = "200" ]; then
              REVIEW=$(echo "$BODY" | python3 -c "import json,sys; print(json.load(sys.stdin)['choices'][0]['message']['content'])")
              gh pr comment "$PR_NUMBER" --body "## 🤖 AI Code Review\n\n${REVIEW}\n\n---\n_Powered by ccplugin-ai-review · Free via OpenRouter_"
              exit 0
            fi
            echo "Model $MODEL returned HTTP $HTTP_CODE, trying next..."
          done
          echo "::error::All OpenRouter models unavailable."
          exit 1

Cost

$0 — uses OpenRouter free tier (Gemma 3 27B Free, Mistral 7B Free fallback).