What Fastify Is

Fastify is a Node.js web framework created by Matteo Collina that benchmarks roughly twice as fast as Express while shipping a richer feature set — JSON Schema validation, plugin encapsulation, and a fast Pino logger out of the box.

Why Fastify

Where Express stays minimal and unopinionated, Fastify makes a few pointed bets: JSON Schema for request validation and response serialization, async hooks for the request lifecycle, and a plugin system with proper encapsulation. The result is a framework that scales from a single file to a large modular service without changing the mental model.

It is used in production at Microsoft, Heroku, Adidas, and many other shops that need both throughput and predictable structure.

The Schema-First Idea

Most frameworks treat validation as middleware you bolt on. Fastify treats it as a route-level declaration:

app.post('/users', {
  schema: {
    body: {
      type: 'object',
      required: ['email'],
      properties: { email: { type: 'string', format: 'email' } },
    },
    response: {
      201: { type: 'object', properties: { id: { type: 'integer' } } },
    },
  },
  handler: async (req, reply) => {
    const user = await createUser(req.body);
    reply.code(201);
    return user;
  },
});

That single schema validates the request body, serializes the response (via fast-json-stringify), and — with @fastify/swagger — generates OpenAPI docs.

The Ecosystem in One Sentence

Encapsulated plugins, request/lifecycle hooks, decorators for shared state, Pino-based structured logging, Ajv 8 validation, and a TypeScript-first developer experience.