Step 2: Project Setup — Build a Code Review Bot

One-Line Summary: Initialize the Node.js project, install the Anthropic SDK and Octokit, and configure TypeScript for building a GitHub Action.

Prerequisites: Node.js 18+ installed, npm

Create the Project

mkdir code-review-bot && cd code-review-bot
npm init -y

Install Dependencies

npm install @anthropic-ai/sdk @octokit/rest @actions/core @actions/github
npm install -D typescript @types/node

What each package does:

Package	Purpose
`@anthropic-ai/sdk`	Official Anthropic TypeScript SDK — sends diffs to Claude and receives structured reviews
`@octokit/rest`	GitHub REST API client — fetches PR diffs, posts review comments
`@actions/core`	GitHub Actions toolkit — read inputs, set outputs, log messages
`@actions/github`	GitHub Actions context — provides the PR number, repo owner, and event payload
`typescript`	TypeScript compiler

Configure TypeScript

Create tsconfig.json:

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "commonjs",
    "moduleResolution": "node",
    "outDir": "./dist",
    "rootDir": "./src",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "declaration": true,
    "resolveJsonModule": true
  },
  "include": ["src/**/*"]
}

We use commonjs modules because GitHub Actions runners expect a standard Node.js require setup. The ES2022 target gives us access to top-level features like Array.prototype.at() and Object.hasOwn().

Update package.json

Add the build script. Open package.json and update it:

{
  "name": "code-review-bot",
  "version": "1.0.0",
  "private": true,
  "scripts": {
    "build": "tsc",
    "start": "node dist/index.js"
  }
}

Create the Source Files

mkdir -p src .github/workflows

Create the type definitions first. Add src/types.ts:

// src/types.ts
// ==========================================
// Shared Type Definitions
// ==========================================
 
// ------------------------------------------
// A single review comment from Claude
// ------------------------------------------
export interface ReviewComment {
  path: string;        // File path relative to repo root
  line: number;        // Line number in the diff
  body: string;        // The review comment text
  severity: "critical" | "warning" | "suggestion";
}
 
// ------------------------------------------
// The complete review result
// ------------------------------------------
export interface ReviewResult {
  summary: string;           // Overall review summary
  comments: ReviewComment[]; // Inline comments on specific lines
  approved: boolean;         // Whether the code looks good overall
}
 
// ------------------------------------------
// A file changed in the pull request
// ------------------------------------------
export interface PullRequestFile {
  filename: string;    // Path relative to repo root
  status: string;      // "added", "modified", "removed", "renamed"
  patch?: string;      // The unified diff for this file
  additions: number;   // Lines added
  deletions: number;   // Lines removed
}

Verify the Setup

npx tsc --version

You should see TypeScript 5.x. Then build the types file to confirm everything compiles:

npx tsc

If there are no errors, your project is ready. The dist/ folder should contain the compiled types.js and types.d.ts.

← What We're Building | Next: Step 3 - GitHub Action Workflow →