Why does ChatGPT and Claude return broken JSON?

LLMs generate text token by token with no syntax checker running during generation. Long JSON responses are more likely to have truncation, missing brackets, or formatting errors. They also wrap JSON in markdown code fences by default.

How do I get clean JSON from an LLM?

Use a system prompt that says "respond only with valid JSON, no markdown, no explanation." Even then, verify with JSONBlitz — LLMs occasionally drop closing brackets on long outputs.

Does JSONBlitz handle markdown code fences around JSON?

Yes. Paste the full LLM response including the ```json fences and JSONBlitz extracts the JSON automatically.

Can JSONBlitz fix truncated LLM output?

If the JSON was cut off before the closing brackets, JSONBlitz closes the open structures. If content is genuinely missing mid-value, that requires regenerating from the LLM.

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Frequently Asked Questions

Why does ChatGPT and Claude return broken JSON?: LLMs generate text token by token with no syntax checker running during generation. Long JSON responses are more likely to have truncation, missing brackets, or formatting errors. They also wrap JSON in markdown code fences by default.
How do I get clean JSON from an LLM?: Use a system prompt that says "respond only with valid JSON, no markdown, no explanation." Even then, verify with JSONBlitz — LLMs occasionally drop closing brackets on long outputs.
Does JSONBlitz handle markdown code fences around JSON?: Yes. Paste the full LLM response including the ```json fences and JSONBlitz extracts the JSON automatically.
Can JSONBlitz fix truncated LLM output?: If the JSON was cut off before the closing brackets, JSONBlitz closes the open structures. If content is genuinely missing mid-value, that requires regenerating from the LLM.