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

Short summary

Constrained decoding and post-hoc validation address different failure modes in production LLM extraction pipelines. Constrained decoding controls generation to reduce malformed payloads and improve schema adherence, while post-hoc validation acts as the trust boundary to coerce, reject, or attach confidence to outputs. The author's rule of thumb: constrain early, validate hard, trust late — both layers are needed because valid JSON can still be semantically wrong for the workflow.

• •Constrained decoding controls generation-time output shape; post-hoc validation is the trust boundary
• •A payload can be valid JSON yet semantically wrong for the workflow
• •Rule of thumb: constrain early, validate hard, trust late

Generated with AI, which can make mistakes.