fastify

Fastify (TypeScript) - Production Backend Framework

Overview

Fastify is a high-performance Node.js web framework built around JSON schema validation, encapsulated plugins, and great developer ergonomics. In TypeScript, pair Fastify with a type provider (Zod or TypeBox) to keep runtime validation and static types aligned.

Quick Start

Minimal server

✅ Correct: basic server with typed response

import Fastify from "fastify";

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

app.get("/health", async () => ({ status: "ok" as const }));

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

❌ Wrong: start server without awaiting listen

app.listen({ port: 3000 });
console.log("started"); // races startup and hides bind failures

Schema Validation + Type Providers

Fastify validates requests/responses via JSON schema. Use a type provider to avoid duplicating types.

Zod provider (recommended for full-stack TypeScript)

✅ Correct: Zod schema drives validation + types

import Fastify from "fastify";
import { z } from "zod";
import { ZodTypeProvider } from "fastify-type-provider-zod";

const app = Fastify({ logger: true }).withTypeProvider<ZodTypeProvider>();

const Query = z.object({ q: z.string().min(1) });

app.get(
  "/search",
  { schema: { querystring: Query } },
  async (req) => {
    return { q: req.query.q };
  },
);

await app.listen({ port: 3000 });

TypeBox provider (recommended for OpenAPI + performance)

✅ Correct: TypeBox schema

import Fastify from "fastify";
import { Type } from "@sinclair/typebox";
import { TypeBoxTypeProvider } from "@fastify/type-provider-typebox";

const app = Fastify({ logger: true }).withTypeProvider<TypeBoxTypeProvider>();

const Params = Type.Object({ id: Type.String({ minLength: 1 }) });
const Reply = Type.Object({ id: Type.String() });

app.get(
  "/users/:id",
  { schema: { params: Params, response: { 200: Reply } } },
  async (req) => ({ id: req.params.id }),
);

await app.listen({ port: 3000 });