jordan macias

Posted on Apr 17

Build Your Own AI Code Review Bot with Claude API and GitHub Actions v2

#programming #tutorial #ai #github

Build Your Own AI Code Review Bot with Claude API and GitHub Actions

Code reviews are essential for maintaining quality, sharing knowledge, and catching bugs before they reach production. But let's be honest—they're also time-consuming. Developers spend hours reviewing pull requests, leaving comments about formatting, potential edge cases, and architectural concerns.

What if you could automate the initial pass? An AI-powered code review bot can handle the routine checks, surface potential issues, and free up your team's time for deeper architectural reviews. In this tutorial, we'll build a production-ready code review bot using Claude's API and GitHub Actions.

Why Claude for Code Review?

Claude excels at code analysis because it understands context, can reason about complex logic, and provides constructive feedback. Unlike simpler linters, Claude can identify subtle logic errors, suggest performance improvements, and even catch security vulnerabilities. The API is straightforward to work with, and Claude's reasoning capabilities make it ideal for nuanced code review tasks.

Architecture Overview

Here's how the system works:

GitHub Action triggers when a pull request is opened or updated
Action fetches the changed files and their diffs
Claude API analyzes the code changes
Bot posts comments on the PR with feedback
Developers review the bot's suggestions alongside human reviews

This approach keeps humans in the loop while automating tedious checks.

Prerequisites

Before we start, you'll need:

A GitHub repository where you can create workflows
A Claude API key (get one at Anthropic's console)
Basic familiarity with GitHub Actions and Node.js
Understanding of git diffs and PR workflows

Step 1: Set Up Your GitHub Action

First, create the workflow file that will trigger our code review bot.

Create .github/workflows/code-review.yml:

name: AI Code Review

on:
  pull_request:
    types: [opened, synchronize, reopened]

jobs:
  review:
    runs-on: ubuntu-latest
    permissions:
      pull-requests: write
      contents: read
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Set up Node.js
        uses: actions/setup-node@v4
        with:
          node-version: '18'

      - name: Install dependencies
        run: npm install

      - name: Run code review
        env:
          CLAUDE_API_KEY: ${{ secrets.CLAUDE_API_KEY }}
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          PR_NUMBER: ${{ github.event.number }}
          REPO_OWNER: ${{ github.repository_owner }}
          REPO_NAME: ${{ github.event.repository.name }}
        run: node review-bot.js

This workflow triggers on pull request events and provides the necessary environment variables to our bot script.

Step 2: Create the Review Bot Script

Now, let's build the core bot logic. Create review-bot.js:

const Anthropic = require("@anthropic-ai/sdk");
const { Octokit } = require("@octokit/rest");

const client = new Anthropic({
  apiKey: process.env.CLAUDE_API_KEY,
});

const octokit = new Octokit({
  auth: process.env.GITHUB_TOKEN,
});

async function getPRDiff() {
  const owner = process.env.REPO_OWNER;
  const repo = process.env.REPO_NAME;
  const prNumber = parseInt(process.env.PR_NUMBER);

  const { data: pr } = await octokit.pulls.get({
    owner,
    repo,
    pull_number: prNumber,
  });

  const { data: files } = await octokit.pulls.listFiles({
    owner,
    repo,
    pull_number: prNumber,
  });

  return { pr, files };
}

async function analyzeCode(diff, filename) {
  const prompt = `You are an expert code reviewer. Analyze the following code changes and provide constructive feedback.

File: ${filename}

Code diff:
\`\`\`
${diff}
\`\`\`

Focus on:
1. Potential bugs or logic errors
2. Performance issues
3. Security vulnerabilities
4. Code style and readability
5. Best practices and patterns

Provide specific, actionable feedback. If the code looks good, say so. Keep feedback concise and professional.`;

  const message = await client.messages.create({
    model: "claude-3-5-sonnet-20241022",
    max_tokens: 1024,
    messages: [
      {
        role: "user",
        content: prompt,
      },
    ],
  });

  return message.content[0].type === "text" ? message.content[0].text : "";
}

async function postReviewComment(feedback, filename) {
  const owner = process.env.REPO_OWNER;
  const repo = process.env.REPO_NAME;
  const prNumber = parseInt(process.env.PR_NUMBER);

  // Only post if there's substantial feedback
  if (feedback.length < 20) {
    return;
  }

  const body = `## 🤖 AI Code Review: ${filename}\n\n${feedback}`;

  await octokit.issues.createComment({
    owner,
    repo,
    issue_number: prNumber,
    body,
  });
}

async function runReview() {
  try {
    console.log("Starting code review...");
    const { pr, files } = await getPRDiff();

    if (!files || files.length === 0) {
      console.log("No files changed in this PR");
      return;
    }

    // Filter to review only code files (adjust based on your needs)
    const codeFiles = files.filter((file) => {
      const ext = file.filename.split(".").pop();
      return [
        "js",
        "ts",
        "jsx",
        "tsx",
        "py",
        "java",
        "go",
        "rb",
        "php",
      ].includes(ext);
    });

    console.log(`Found ${codeFiles.length} code files to review`);

    for (const file of codeFiles) {
      console.log(`Reviewing ${file.filename}...`);

      // Skip deleted files
      if (file.status === "removed") {
        continue;
      }

      // Get the actual diff content
      const { data: fileContent } = await octokit.repos.getContent({
        owner: process.env.REPO_OWNER,
        repo: process.env.REPO_NAME,
        path: file.filename,
        ref: pr.head.sha,
      });

      const feedback = await analyzeCode(file.patch, file.filename);
      await postReviewComment(feedback, file.filename);

      // Be respectful to API rate limits
      await new Promise((resolve) => setTimeout(resolve, 1000));
    }

    console.log("Code review completed!");
  } catch (error) {
    console.error("Error during code review:", error);
    process.exit(1);
  }
}

runReview();

Step 3: Set Up Dependencies

Create a package.json file:

{
  "name": "ai-code-review-bot",
  "version": "1.0.0",
  "description": "AI-powered code review bot using Claude API",
  "main": "review-bot.js",
  "scripts": {
    "test": "node review-bot.js"
  },
  "dependencies": {
    "@anthropic-ai/sdk": "^0.16.0",
    "@octokit/rest": "^20.0.0"
  }
}

Install dependencies:

npm install

Step 4: Configure GitHub Secrets

Your bot needs API credentials to function. Add your Claude API key to GitHub:

Go to your repository's Settings
Navigate to Secrets and variables → Actions
Click "New repository secret"
Add CLAUDE_API_KEY with your API key from Anthropic's console

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