JSON Kit is a set of fast, browser-side JSON tools built for the AI era. The standout is Fix LLM JSON: paste the broken JSON that ChatGPT, Claude, or local models hand you, and get clean, valid JSON back instantly, with a label for exactly what was wrong (trailing commas, single quotes, Python literals, markdown fences, truncated output, and more). Everything runs 100% in your browser, so your output never touches a server.

Hey Product Hunt 👋 I built JSON Kit. This started from one annoying bug. I kept piping LLM output into JSON.parse() and it would work fine for days, then break in production because the model added a trailing comma or wrapped everything in a ```json fence. If you've built anything on top of AI output you've probably hit the exact same thing. So I made Fix LLM JSON: paste the broken stuff, get clean JSON back, and it tells you what was wrong instead of silently fixing it. It runs entirely in your browser, which I cared about because LLM outputs are full of API keys and user data I didn't want sending anywhere. Full transparency: the repair engine under the hood is the open-source jsonrepair library by Jos de Jong, with a layer I built on top to detect and label the specific error patterns. The rest of the kit (formatter, JSON→TS, JSON→Zod, JSONPath, diff, markdown extractor) grew out of the same "I keep needing this" itch. It's free to use, no signup. Would genuinely love feedback on what else breaks your JSON, especially the weird edge cases. Happy to answer anything in the comments today.

"Fix LLM JSON" is the differentiator but the description lists the categories of errors it handles (trailing commas, single quotes, etc.) — does it also catch semantic errors? Like if Claude outputs valid JSON syntactically but with a wrong field name or type, does it flag that too or only structural issues?

JSON Kit

Fix broken AI JSON and 6 more JSON tools, all in-browser

Fix broken AI JSON and 6 more JSON tools, all in-browser