Fastify Best Practices

When to use

Use this skill when you need to:

• Develop backend applications using Fastify
• Implement Fastify plugins and route handlers
• Get guidance on Fastify architecture and patterns
• Use TypeScript with Fastify (strip types)
• Implement testing with Fastify's inject method
• Configure validation, serialization, and error handling

Quick Start

A minimal, runnable Fastify server to get started immediately:

import Fastify from 'fastify'

const app = Fastify({ logger: true })

app.get('/health', async (request, reply) => {
  return { status: 'ok' }
})

const start = async () => {
  await app.listen({ port: 3000, host: '0.0.0.0' })
}
start()

Recommended Reading Order for Common Scenarios

• New to Fastify? Start with plugins.md → routes.md → schemas.md
• Adding authentication: plugins.md → hooks.md → authentication.md
• Improving performance: schemas.md → serialization.md → performance.md
• Setting up testing: routes.md → testing.md
• Going to production: logging.md → configuration.md → deployment.md

How to use

Read individual rule files for detailed explanations and code examples:

• rules/plugins.md - Plugin development and encapsulation
• rules/routes.md - Route organization and handlers
• rules/schemas.md - JSON Schema validation
• rules/error-handling.md - Error handling patterns
• rules/hooks.md - Hooks and request lifecycle
• rules/authentication.md - Authentication and authorization
• rules/testing.md - Testing with inject()
• rules/performance.md - Performance optimization
• rules/logging.md - Logging with Pino
• rules/typescript.md - TypeScript integration
• rules/decorators.md - Decorators and extensions
• rules/content-type.md - Content type parsing
• rules/serialization.md - Response serialization
• rules/cors-security.md - CORS and security headers
• rules/websockets.md - WebSocket support
• rules/database.md - Database integration patterns
• rules/configuration.md - Application configuration
• rules/deployment.md - Production deployment
• rules/http-proxy.md - HTTP proxying and reply.from()

Core Principles

• Encapsulation: Fastify's plugin system provides automatic encapsulation
• Schema-first: Define schemas for validation and serialization
• Performance: Fastify is optimized for speed; use its features correctly
• Async/await: All handlers and hooks support async functions
• Minimal dependencies: Prefer Fastify's built-in features and official plugins