Module
Module 3 of 6Lesson 2 of 2~15 min

Let the model say "I don't know" in the schema

Lesson 2 of the module "Design the schema" in the course "Get reliable, product-ready AI outputs (JSON, schemas, function calling)".

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Lesson objective

By the end of this lesson, you will be able to plan in a schema how to express missing information (null, "unknown" value, extraction status), choose the order of fields and judge the use of a confidence score.

Where it fits

Design the schema

Which fields, which types and which allowed values, and how do I let the model say "I don't know"?

Lessons in this module

  1. Write the spec of every field in the schema
  2. Let the model say "I don't know" in the schema (this lesson)

What you will learn in the course

This lesson is part of the course Get reliable, product-ready AI outputs (JSON, schemas, function calling)

  • Diagnose where free-text output breaks a feature and decide which outputs require a contract.
  • Choose between instructions alone, JSON mode, structured outputs and function calling for a given need, and justify the choice.
  • Design an output schema (types, enums, required fields, nullable fields, descriptions, "unknown" values) where every field serves a consumer.
  • Specify validation (syntax, schema, business rules), retries, handling of refusals and truncation, and the fallback path.
  • Version and evolve an output contract without breaking its consumers, accounting for provider differences and the split of roles between PM and developers.
  • Build a set of 20 robustness cases and set acceptance thresholds before going to production.

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