FREE TOOL · ON YOUR DEVICE
Format and validate JSON for free
Paste JSON or choose a UTF-8 file to check syntax and adjust its presentation. Numbers remain lexemes: a large integer or long decimal is never rounded by conversion to Number. Content stays on your device.
- Free with an account
- Exact numbers
- Duplicate key warnings
- Enter JSON
- Validate and format
- Review warnings
HOW TO USE IT
Three steps.
Enter JSON
Paste the document or choose a UTF-8 file up to 1 MiB. A selected file takes priority.
Validate and format
Choose two spaces, four spaces or compact output. Up to 100 levels and 200,000 nodes are supported.
Review warnings
Correct errors by line and column. Review repeated keys before copying or downloading JSON.
NEXT STEP
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Format and validate JSON: common questions
Are large integers and decimals preserved?
Yes. The original number lexeme is kept without conversion to Number; string escapes are also preserved.
What happens with duplicate keys?
A warning is shown and every key remains in output. Other readers may keep only one; CSV conversion requires fixing duplicates first.
Does it validate JSON5 or a schema?
No. It checks JSON syntax; comments, trailing commas and JSON5 are unsupported, and it does not check schema rules. Output is limited to 4 MiB.
Is my text sent to a server?
No. Everything is calculated in your browser as you type; the text is not sent to Cocuyo or any third party and is not stored. You can check it in your browser’s network tools: your file is not sent.
Is it really free?
Yes. You can try it before signing up; to keep using it, we ask for a free account, with no subscription. It uses no credits and does not count toward your 30 welcome uses: it has no usage cap.
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