How do you get reliable structured (e.g. JSON) output from an LLM?

Prefer the provider's structured-output or tool-calling mode with a JSON schema, which constrains generation, rather than asking for JSON in prose. Then validate the result against the schema and retry on failure. Reinforce with a clear example of the exact shape, put the format instruction near the end, and set low temperature. Never regex JSON out of a chatty answer in production — schema-enforced output eliminates an entire class of parsing failures.