# Response Serialization — Fastify

Source: https://www.geekswithgeeks.com/en/fastify/ff-serialization

> Control how responses are serialized to JSON for performance.

## Schema-based serialization

The `response` field in schema tells Fastify what fields to send, speeding up JSON serialization by only including declared properties.

## Response schema

Define what the response looks like. Fastify will only serialize fields in the schema.

```javascript
const getUserSchema = {
  response: {
    200: {
      type: 'object',
      properties: {
        id: { type: 'integer' },
        name: { type: 'string' },
        email: { type: 'string' },
      },
    },
  },
};

fastify.get('/users/:id', { schema: getUserSchema }, async (req) => {
  return {
    id: 1,
    name: 'Alice',
    email: 'alice@example.com',
    // password field will be stripped by serialization
  };
});
```