Route Handlers & Status Codes

Async handlers return data

Fastify handlers are async functions. Return an object and Fastify auto-serializes it to JSON and sends 200 OK.

Custom status codes

Use reply.code() or reply.status() to set a custom HTTP status before sending.

fastify.post('/items', async (req, reply) => {
  const item = { id: 1, name: 'Widget' };
  return reply.code(201).send(item);
});

fastify.get('/missing', async (req, reply) => {
  return reply.code(404).send({ error: 'Not found' });
});

fastify.delete('/items/:id', async (req, reply) => {
  return reply.code(204).send();
});

Handler options (schema, auth, etc.)

Fastify routes accept an optional third argument with metadata—schema for validation, auth for permission checks.