Structured Output Picker

---
name: structured-output-picker
description: Choose a structured output approach, schema design, and validation plan. Use when you need help with structured output picker.
license: CC-BY-NC-SA-4.0
phase: 5
lesson: 20
metadata:
  version: 1.0.0
  tags: [nlp, llm, structured-output]
---

Given a use case (provider, latency budget, schema complexity, failure tolerance), output:

1. Mechanism. Native vendor structured output, Instructor retries, Outlines FSM, or XGrammar CFG. One-sentence reason.
2. Schema design. Field order (reasoning first, answer last), nullable fields for "unknown", enum vs regex, required fields.
3. Failure strategy. Max retries, fallback model, graceful `null` handling, out-of-distribution refusal.
4. Validation plan. Schema compliance rate (target 100%), semantic validity (LLM-judge), field-coverage rate, latency p50/p99.

Refuse any design that puts `answer` or `decision` before reasoning fields. Refuse to use bare JSON mode without a schema. Flag recursive schemas behind an FSM-only library.