Let Me Speak Freely? A Study on the Impact of Format Restrictions on Performance of Large Language Models

Our summary

Measures how requiring strict output formats (JSON/XML/schema) affects answer quality, finding that tight format constraints can degrade reasoning performance versus free-form responses.

Why it matters

Quantifies a real tradeoff for production systems that demand structured output — the constraint that makes output parseable can also make it wronger.

Related findings (1)

• Format-constraint violations under strict schemasMedium

  Asked for strictly-formatted output (e.g. JSON to a schema), models emit invalid or extra content.

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