# GitHub Code Review Apps & Tools

An overview of the code review ecosystem for GitHub. Depth of explanation adapts to user skill level.

## Why Automated Code Review?

**Beginner framing:** "These apps watch your pull requests and give feedback automatically — like having a senior developer review your code 24/7. They catch bugs, suggest improvements, and help you learn."

**Intermediate framing:** "Automated review tools complement human reviewers by catching patterns humans miss: security issues, performance problems, style inconsistencies. They run on every PR automatically."

**Advanced framing:** "These integrate into your PR workflow via GitHub Apps or Actions. They post inline comments, block merges on critical findings, and reduce review burden on your team."

## Tools Overview

### CodeRabbit

**What it does:** AI-powered code review that posts detailed, contextual inline comments on PRs. Understands the full context of changes, not just syntax.

**Key features:**

- Inline PR comments with explanations and fix suggestions
- Understands project context and patterns
- Configurable review depth and focus areas
- Supports 20+ languages

**Best for:** Teams that want comprehensive AI review with actionable feedback.

**Setup:** Install the GitHub App from github.com/apps/coderabbitai. Configure via `.coderabbit.yaml` in repo root.

**Hands-on exercise (intermediate):** Walk through installing CodeRabbit on a repo, creating a test PR, and reading the review comments.

### GitHub Copilot Code Review

**What it does:** GitHub's built-in AI review, integrated directly into the PR interface. Powered by the same models behind GitHub Copilot.

**Key features:**

- Native GitHub integration — no extra app to install
- Suggests code improvements inline
- Available with GitHub Copilot subscription

**Best for:** Teams already using GitHub Copilot who want review integrated into their existing workflow.

**Setup:** Enable in repository settings under Copilot features (requires Copilot subscription).

### Greptile

**What it does:** AI code review that builds a deep understanding of your codebase. Goes beyond single-file review to understand architectural patterns and cross-file dependencies.

**Key features:**

- Codebase-aware review (understands how files relate)
- Catches architectural issues, not just syntax
- Natural language explanations

**Best for:** Larger codebases where cross-file context matters for review quality.

**Setup:** Install via GitHub App. Indexes your codebase for contextual understanding.

### CodeQL (GitHub Advanced Security)

**What it does:** Static analysis that finds security vulnerabilities and bugs by treating code as data. Queries the code structure to find patterns that match known vulnerability classes.

**Key features:**

- Security-focused: finds SQL injection, XSS, auth bypass, etc.
- Runs as GitHub Actions workflow
- Free for public repositories
- Includes SARIF reporting for security dashboards

**Best for:** Security-conscious teams, open-source projects, and anyone shipping code that handles user data.

**Setup:** Add `.github/workflows/codeql.yml` to your repo. GitHub provides starter workflows.

**Beginner note:** "CodeQL is like a security guard for your code. It checks for common security mistakes that could let hackers in."

### Qodo (formerly CodiumAI)

**What it does:** AI-powered test generation and code review. Focuses on suggesting tests for your changes and finding edge cases.

**Key features:**

- Auto-generates test suggestions for PRs
- Identifies untested edge cases
- Reviews code for potential bugs
- IDE integration (VS Code, JetBrains)

**Best for:** Teams that want to improve test coverage alongside code review.

**Setup:** Install the GitHub App or IDE extension.

## Comparison Matrix

| Tool | Focus | Cost (Public Repos) | Setup Effort | Review Style |
|------|-------|--------------------|--------------|----|
| CodeRabbit | Comprehensive AI review | Free tier available | Low (GitHub App) | Inline comments |
| Copilot Review | General AI review | Copilot subscription | Minimal (built-in) | Inline suggestions |
| Greptile | Codebase-aware review | Free tier available | Low (GitHub App) | Contextual comments |
| CodeQL | Security vulnerabilities | Free | Medium (Actions workflow) | Security alerts |
| Qodo | Test generation + review | Free tier available | Low (GitHub App) | Test suggestions |

## Recommendations by Skill Level

**Beginner:** Start with Copilot Code Review (if available) or CodeRabbit. Both are easy to set up and provide clear, actionable feedback that helps you learn.

**Intermediate:** Add CodeQL for security scanning. Start reading review comments critically — understand why each suggestion is made, not just whether to accept it.

**Advanced:** Layer multiple tools. Use CodeRabbit or Greptile for general review, CodeQL for security, and Qodo for test coverage gaps. Configure review rules to match your team's standards.

**Expert:** Evaluate tools based on signal-to-noise ratio for your codebase. Consider custom CodeQL queries for domain-specific patterns. Integrate review tools into your CI/CD pipeline as merge gates.
