---

name: bun-patterns description: Verify Bun-specific patterns in backend code. Use when reviewing or writing backend TypeScript files to ensure Bun APIs are used instead of Node.js patterns. allowed-tools: Read, Grep, Glob

Bun Patterns Verification

Automatically check that backend code uses Bun-specific APIs instead of Node.js patterns.

When to Apply

• Reviewing files in src/backend/
• Writing new backend code
• Checking file I/O operations

Patterns to Enforce

File Operations

Correct (Bun):

Copy// Reading files
const content = await Bun.file(path).text();
const json = await Bun.file(path).json();

// Writing files
await Bun.write(path, content);

// Checking existence
const exists = await Bun.file(path).exists();

Incorrect (Node.js):

Copy// These should NOT be used in backend
import fs from 'fs';
import { readFile, writeFile } from 'fs/promises';
fs.readFileSync(path);

Process and Environment

Correct (Bun):

Copyconst port = Bun.env.PORT || 9339;

Incorrect:

Copyconst port = process.env.PORT; // Less preferred in Bun

HTTP Server

Correct (Bun):

CopyBun.serve({
  port: 9339,
  fetch(req) {
    return new Response('OK');
  },
});

Verification Steps

1. Search for Node.js imports: import fs from, require('fs')
2. Check file operations use Bun.file() or Bun.write()
3. Verify WebSocket server uses Bun patterns
4. Confirm no fs.readFile or fs.writeFile calls

Reference

• Bun File I/O
• Bun HTTP Server
• Project Rule 2 in CLAUDE.md