Type Providers with TypeBox

One schema, two benefits

Writing JSON Schema and TypeScript types separately invites drift. A type provider such as @fastify/type-provider-typebox infers handler types from the schema, so validation and types always match.

Typed route

The schema both validates the request and types request.body.

import Fastify from 'fastify';
import { Type, TypeBoxTypeProvider } from '@fastify/type-provider-typebox';

const app = Fastify().withTypeProvider<TypeBoxTypeProvider>();

app.post('/items', {
  schema: { body: Type.Object({ name: Type.String(), price: Type.Number({ minimum: 0 }) }) },
}, async (req) => {
  return { name: req.body.name.toUpperCase() }; // req.body is typed
});

Keep response schemas too: they speed up serialization and stop accidental data leaks.