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Cortex · Output

Custom validation (output.validate)

output.validate is a custom validation function for rules the output schema cannot express. When it returns { retry }, the run emits a retry event and sends the reason to the model in the same run, then validates the next output again. The model’s two turns are scripted, the first with a night that has no show; no model is called.

Agent and validation
const Order = z.object({ night: z.string(), seats: z.number().int() });
const NIGHTS = ['2026-10-23', '2026-10-24', '2026-10-25'];

const clerk = defineAgent({
  id: 'clerk',
  instructions: 'Read what the member wants into an order.',
  output: {
    schema: Order,
    validate: ({ data }) =>
      NIGHTS.includes(data.night)
        ? { ok: true }
        : { retry: `nothing plays on ${data.night}, only on ${NIGHTS.join(', ')}` },
  },
});

const result = await clerk.run('Two seats for Sunday, please.', { llm }).result;
Run, attempt by attempt
Scripted model turn
writes {"data":{"night":"2026-10-26","seats":2}}
Event
{
  type: 'retry',
  kind: 'output',
  attempt: 1,
  issues: 'nothing plays on 2026-10-26, only on 2026-10-23, 2026-10-24, 2026-10-25',
}
Output matches the expected value

Runs in this page on the installed package. The input and the expected output are defined by the example.