The token overhead of forcing JSON / structured responses.
The token cost of JSON mode is small next to the cost of parsing flaky free-text output. Keep schemas lean and it's a bargain. Estimate the whole call on the LLM token cost calculator.
The Structured Output (JSON) Cost Calculator estimates the monthly API spend of getting model responses in a structured JSON format. You enter your calls per month, the tokens consumed by the JSON schema and other input on each call, the output tokens per call, and your input and output prices per million tokens. It multiplies each token count by its rate and by your call volume to produce a monthly figure. The point it makes concrete is that structured output is not free: the schema definition, field names, and formatting instructions all add input tokens to every call, and rigidly formatted responses often carry more output tokens than plain text would.
The key trade-off is between reliability and cost. A detailed schema makes responses easier to parse and validate, but because those schema tokens repeat on every single call, they scale directly with volumeβa small per-call overhead becomes a large line item at millions of calls. The practical lever is to keep schemas lean: use short field names, drop unnecessary descriptions, and avoid deeply nested structures you never read. Separate the two figures the calculator reports, since input and output are usually priced differently, and check whether trimming schema verbosity or output length moves your total more. Run a few scenarios before committing a format across your whole workload.
A little. You send the JSON schema as extra input tokens, and structured responses tend to be more verbose than free text. On high volume that adds up, though it usually pays for itself in fewer parsing errors.
Almost always β reliable, parseable output saves engineering time and failed requests. Just keep the schema minimal and don't request fields you won't use.