fastify

name	fastify
description	Guides AI agents to write correct, idiomatic Fastify code using plugins, routes, schemas, and lifecycle hooks.
metadata	{"tags":["fastify","nodejs","http","api"]}

Fastify Skill

Use this skill when writing or reviewing any Fastify server code: route definitions, plugins, request validation, error handling, or server lifecycle.

When to Use

• Creating a Fastify server or adding routes
• Writing or registering a Fastify plugin
• Defining request/reply JSON schemas
• Handling errors and reply serialization
• Using hooks (onRequest, preHandler, onSend, etc.)
• Decorating the Fastify instance or request/reply objects

Rules

1. rules/plugins.md — Plugin authoring, fastify-plugin, encapsulation, registration order.
2. rules/routes.md — Route definitions, shorthand methods, async handlers, reply usage.
3. rules/schemas.md — JSON Schema for request validation and reply serialization with $ref.
4. rules/hooks.md — Lifecycle hooks, execution order, and correct async usage.
5. rules/error-handling.md — setErrorHandler, httpErrors, and safe error propagation.

Quick Reference

// Minimal idiomatic server
import Fastify from 'fastify';

const app = Fastify({ logger: true });

app.register(import('./routes/users.js'));

await app.listen({ port: 3000, host: '0.0.0.0' });

// Route with schema
app.post('/users', {
  schema: {
    body: { $ref: 'CreateUserBody#' },
    response: { 201: { $ref: 'User#' } },
  },
  handler: async (request, reply) => {
    const user = await createUser(request.body);
    return reply.code(201).send(user);
  },
});