Constrained Decoding vs Post-hoc Validation: Production LLM Extraction Needs Both

Constrained decoding and post-hoc validation solve different problems.

Constrained decoding is generation-time control:

• fewer malformed payloads


• less wrapper text


• better adherence to schema/tool shape

Post-hoc validation is the trust boundary:

• coerce what is safe


• reject what is not


• attach confidence where routing matters

A payload can be perfectly valid JSON and still be wrong for the workflow.

That is why production extraction systems need both.

This is also the systems instinct behind .

My rule of thumb:

Constrain early. Validate hard. Trust late.