Simple scheme using fastify

schema.js

const schema = {
  response: {
    '2xx': {
      type: 'object',
      properties: {
        value: { type: 'string' },
        otherValue: { type: 'boolean' }
      }
    },
    201: {
      type: 'object',
      properties: {
        value: { type: 'string' }
      }
    }
  }
}

fastify.post('/the/url', { schema }, handler)