+handler.ts

import type { FastifyPluginAsyncTypebox } from '@fastify/type-provider-typebox';
import { Type } from '@sinclair/typebox';

export default (async (app) => {
  /*
  $ curl --request GET \
         --url http://127.0.0.1:3000/api/hello-world
  */
  app.get(
    '',
    {
      schema: {
        response: {
          200: Type.Object({
            message: Type.String(),
          }),
        },
      },
    },
    async (req, reply) => {
      return reply.send({
        message: 'Hello, World!',
      });
    },
  );
}) as FastifyPluginAsyncTypebox;