/gemini-review

name: gemini-review
description: Google Gemini CLI code review with Gemini 2.5 Pro, 1M token context, CI/CD integration
when-to-use: When user requests Gemini-powered code review or needs large-context review
user-invocable: true
effort: medium

Google Gemini Code Review Skill

Use Google's Gemini CLI for code review with Gemini 2.5 Pro - featuring a massive 1M token context window that can analyze entire repositories at once.

**Sources:** [Gemini CLI](https://github.com/google-gemini/gemini-cli) | [Code Review Extension](https://github.com/gemini-cli-extensions/code-review) | [Gemini Code Assist](https://codeassist.google/) | [GitHub Action](https://github.com/google-github-actions/run-gemini-cli)

---

Why Gemini for Code Review?

| Feature | Benefit | |---------|---------| | **Gemini 2.5 Pro** | State-of-the-art reasoning for code | | **1M token context** | Entire repositories fit - no chunking needed | | **Free tier** | 1,000 requests/day with Google account | | **Consistent output** | Clean formatting, predictable structure | | **GitHub native** | Gemini Code Assist app for auto PR reviews |

Benchmark Performance

| Benchmark | Score | Notes | |-----------|-------|-------| | SWE-Bench Verified | 63.8% | Agentic coding benchmark | | Qodo PR Benchmark | 56.3% | PR review quality | | LiveCodeBench v5 | 70.4% | Code generation | | WebDev Arena | #1 | Web development |

---

Installation

Prerequisites

# Check Node.js version (requires 20+)
node --version

# Install Node.js 20 if needed
# macOS
brew install node@20

# Or via nvm
nvm install 20
nvm use 20

Install Gemini CLI

# Via npm (recommended)
npm install -g @google/gemini-cli

# Via Homebrew (macOS)
brew install gemini-cli

# Or run without installing
npx @google/gemini-cli

# Verify installation
gemini --version

Install Code Review Extension

# Requires Gemini CLI v0.4.0+
gemini extensions install https://github.com/gemini-cli-extensions/code-review

# Verify extension
gemini extensions list

---

Authentication

Option 1: Google Account (Recommended)

**Free tier: 1,000 requests/day, 60 requests/min**

# Run gemini and follow browser login
gemini

# Select: "Login with Google Account"
# Opens browser for OAuth

This gives you access to Gemini 2.5 Pro with the full 1M token context window.

Option 2: Gemini API Key

**Free tier: 100 requests/day**

# Get API key from https://aistudio.google.com/apikey

# Set environment variable
export GEMINI_API_KEY="your-api-key"

# Or add to shell profile
echo 'export GEMINI_API_KEY="your-api-key"' >> ~/.zshrc

# Run Gemini
gemini

Option 3: Vertex AI (Enterprise)

# For Google Cloud projects
export GOOGLE_API_KEY="your-api-key"
export GOOGLE_GENAI_USE_VERTEXAI=true
export GOOGLE_CLOUD_PROJECT="your-project-id"

gemini

---

Interactive Code Review

Using the Code Review Extension

# Start Gemini CLI
gemini

# Run code review on current branch
/code-review

The extension analyzes:

• Code changes on your current branch
• Identifies quality issues
• Suggests fixes

Manual Review Prompts

# In interactive mode
gemini

# Then ask:
> Review the changes in this branch for bugs and security issues
> Analyze src/api/users.ts for potential vulnerabilities
> What are the code quality issues in the last 3 commits?

---

Headless Mode (Automation)

Basic Usage

# Simple prompt execution
gemini -p "Review the code changes for bugs and security issues"

# With JSON output (for parsing)
gemini -p "Review the changes" --output-format json

# Stream JSON events (real-time)
gemini -p "Review and fix issues" --output-format stream-json

# Specify model
gemini -m gemini-2.5-pro -p "Deep code review of this PR"

Full CI/CD Example

# Get diff and review
git diff origin/main...HEAD > diff.txt

gemini -p "Review this code diff for:
1. Security vulnerabilities
2. Performance issues
3. Code quality problems
4. Missing error handling

Diff:
$(cat diff.txt)
" --output-format json > review.json

Session Tracking

# Track token usage and costs
gemini -p "Review changes" --session-summary metrics.json

# View metrics
cat metrics.json

---

GitHub Integration

Option 1: Gemini Code Assist App (Easiest)

Install from [GitHub Marketplace](https://github.com/marketplace/gemini-code-assist):

1. Go to GitHub Marketplace → Gemini Code Assist 2. Click "Install" and select repositories 3. PRs automatically get reviewed when opened

**Commands in PR comments:**

/gemini review     # Request code review
/gemini summary    # Get PR summary
/gemini help       # Show available commands

**Quota:**

• Free: 33 PRs/day
• Enterprise: 100+ PRs/day

Option 2: GitHub Action

# .github/workflows/gemini-review.yml
name: Gemini Code Review

on:
  pull_request:
    types: [opened, synchronize]

jobs:
  review:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      pull-requests: write

    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Setup Node.js
        uses: actions/setup-node@v4
        with:
          node-version: '20'

      - name: Install Gemini CLI
        run: npm install -g @google/gemini-cli

      - name: Run Review
        env:
          GEMINI_API_KEY: ${{ secrets.GEMINI_API_KEY }}
        run: |
          # Get diff
          git diff origin/${{ github.base_ref }}...HEAD > diff.txt

          # Run Gemini review
          gemini -p "Review this pull request diff for bugs, security issues, and code quality problems. Be specific about file names and line numbers.

          $(cat diff.txt)" > review.md

      - name: Post Review Comment
        uses: actions/github-script@v7
        with:
          script: |
            const fs = require('fs');
            const review = fs.readFileSync('review.md', 'utf8');
            github.rest.iss