Structured Output (JSON Mode): When to Force It and When to Just Ask

If you're going to parse a model's response with code, ask for structured output (JSON mode / a schema) rather than parsing free text — regex-ing a response apart is a maintenance trap that breaks the moment the model rephrases something. When to force it: - Anything downstream is a program, not a person — an API response, a database write, a function call's arguments. - You need a fixed set of fields every time, even when some are empty/null — structured output makes "missing" explicit instead of ambiguous. When to skip it: - The output is meant to be read by a person — prose reads better than a JSON blob, and forcing structure can make explanations more stilted. - The task is genuinely open-ended (brainstorming, long-form writing) — a rigid schema fights against what you're actually asking for. One practical note: schema-constrained generation can very slightly reduce quality on the actual content versus letting the model write freely, because it's now also managing syntax. For anything where the content quality matters more than machine-readability, consider generating prose first and extracting structure in a second pass instead of forcing both at once.