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Parse JSON From LLM Output: Code Fences, Extra Prose, Trailing Commas, Single Quotes and Truncation

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Self-Hosting & Infra intermediate 7 min read $0.01 Updated 2026-10-20

Thirteen malformed inputs run through json.loads with their error messages, plus a tested extractor using JSONDecoder.raw_decode, a trailing-comma regex and its failure inside strings, strict=False for newlines, and a validate-then-retry loop.

Models wrap JSON in markdown fences, add commentary, use Python literals or get cut off. See the exact json.loads error for each, extract with raw_decode, fix safe cases, and know when to retry instead of repairing.

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#llm#json#parsing#structured-output#python

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