Prompting Techniques for Reliable JSON: Schema-in-Prompt & Few-Shot Examples
~15 min read
Three compounding techniques for getting reliable JSON: put the exact schema in the prompt, add few-shot examples for edge cases, and use the API's native JSON/structured-output mode when available.
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Key points
- •Technique 1 — schema-in-prompt: spell out exact field names and types (string, number, boolean, array, enum) to remove structural ambiguity
- •Technique 2 — few-shot examples: show 1-3 input/output pairs to pin down edge-case behavior the schema alone can't fully specify
- •Technique 3 — native JSON/structured-output mode: constrains decoding itself to only emit valid JSON, a structural guarantee beyond prompting
- •Prompting alone can still be ignored by the model; native JSON mode structurally cannot emit invalid syntax
- •The most reliable pipelines stack all three: schema + few-shot examples + API-level JSON mode as a backstop