claude-code - 💡(How to fix) Fix output_config.format returns 400 'compiled grammar is too large' with no documented limits [1 participants]

This limit was discovered empirically through trial and error. There is no documentation on: Documentation should specify grammar size limits and how schema features contribute to compiled size. Ideally, the error message should indicate which part of the schema is causing the limit to be exceeded, or provide an estimated vs. maximum grammar size.

TL;DR

To mitigate the "compiled grammar is too large" error, simplify the JSON schema by reducing optional parameters, avoiding large enums, and flattening nested objects.

Guidance

• Review the schema for optional fields and consider making them required to reduce the FSM state space.
• Limit the use of large enums (over 100 values) and maxItems on arrays, as these contribute to increased grammar size.
• Remove description fields from the schema before passing it to the API, as they may increase raw schema size.
• Consider flattening deeply nested objects to reduce grammar size.

Example

No code snippet is provided as the issue does not contain specific code examples.

Notes

The exact grammar size limit and how schema features contribute to it are not documented, making it challenging to estimate whether a given schema will compile successfully. The provided workaround may not be suitable for all use cases, especially those requiring optional fields or large enums.

Recommendation

Apply the workaround by simplifying the schema, as there is no clear indication of a fixed version that addresses this issue. This approach can help mitigate the error, but it may require significant changes to the schema design.