Fastify Has a Free API You Should Know About

Fastify is the fastest Node.js web framework, and its plugin architecture makes it far more than a simple HTTP server.

Core API — Speed Meets Simplicity

import Fastify from 'fastify'

const fastify = Fastify({ logger: true })

fastify.get('/api/users', async (request, reply) => {
  const { limit = 10, offset = 0 } = request.query
  return db.user.findMany({ take: limit, skip: offset })
})

fastify.post('/api/users', {
  schema: {
    body: {
      type: 'object',
      required: ['name', 'email'],
      properties: {
        name: { type: 'string' },
        email: { type: 'string', format: 'email' }
      }
    }
  }
}, async (request) => {
  return db.user.create({ data: request.body })
})

await fastify.listen({ port: 3000 })

JSON Schema Validation — Free Performance

Fastify validates AND serializes using JSON Schema, making it 2-3x faster than Express:

const userSchema = {
  type: 'object',
  properties: {
    id: { type: 'string' },
    name: { type: 'string' },
    email: { type: 'string' },
    createdAt: { type: 'string', format: 'date-time' }
  }
}

fastify.get('/api/users/:id', {
  schema: {
    params: { type: 'object', properties: { id: { type: 'string' } } },
    response: { 200: userSchema }
  }
}, async (request) => {
  return db.user.findUnique({ where: { id: request.params.id } })
})

Plugin System — Encapsulated Modules

async function authPlugin(fastify) {
  fastify.decorateRequest('user', null)
  fastify.addHook('preHandler', async (request) => {
    const token = request.headers.authorization?.replace('Bearer ', '')
    if (token) request.user = await verifyJWT(token)
  })
}

async function usersRoutes(fastify) {
  fastify.register(authPlugin)
  fastify.get('/', async (req) => {
    if (!req.user) throw fastify.httpErrors.unauthorized()
    return db.user.findMany()
  })
}

fastify.register(usersRoutes, { prefix: '/api/users' })

Real-World Use Case

A team migrated from Express to Fastify for their API gateway handling 10K req/sec. JSON Schema validation replaced 200 lines of Joi validators. Response serialization alone cut p95 latency from 45ms to 18ms. Same logic, half the code, twice the speed.

Fastify proves that "fast" and "easy" aren't opposites.

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