Cortex · Tools and gates

Invalid tool arguments (`input_invalid`)

A tool call whose arguments fail the tool’s input schema produces an observation of kind error with code input_invalid. Arguments are parsed before execute, so execute is not called; the model receives the validation message as the tool result and the run continues. Here the model requests eight seats and the schema allows six; its turns are scripted and no model is called.

Tool and agent

const book = defineTool({
  id: 'book',
  name: 'book',
  description: 'Book seats for the member on a night',
  riskLevel: 'medium',
  input: z.object({ night: z.string(), seats: z.number().int().min(1).max(6) }),
  execute: ({ night, seats }) => {
    made.bookings += 1;
    return { night, seats, left: seatsLeftOn(night) - seats };
  },
});

const desk = defineAgent({
  id: 'desk',
  instructions: 'Book what the member asks for.',
  tools: [book],
});

const result = await desk.run('Eight seats for Sunday, please.', { llm }).result;

Scripted model turns

1  calls book {"night":"2026-10-25","seats":8}
2  writes {"response":"I can book six seats at most in one go. Shall I book six?"}

Output

{
  observation: {
    kind: 'error',
    toolId: 'book',
    args: { night: '2026-10-25', seats: 8 },
    error: 'input_invalid: seats: Too big: expected number to be <=6',
  },
  toolResult: 'error: input_invalid: seats: Too big: expected number to be <=6',
  bookingsMade: 0,
  result: {
    ok: true,
    output: {
      response: 'I can book six seats at most in one go. Shall I book six?',
    },
  },
}

Output matches the expected value

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

Invalid tool arguments (input_invalid)

Invalid tool arguments (`input_invalid`)