JSON Validator
Know your JSON is valid before shipping.
Runs on your deviceJSON
At a glance
- Input:
- JSON
- Processing:
- Runs locally in your browser
- Privacy:
- Your files stay on your device — nothing is uploaded to a server
About this tool
A strict-but-friendly validator that reports the first syntax error precisely, warns about duplicate keys and summarizes document shape.
How to use it
- Paste your JSON.
- Validation runs automatically.
- Fix issues guided by exact positions.
Frequently asked questions
What does validation check?
Syntax validity against RFC 8259, duplicate object keys (a silent bug source), maximum nesting depth, and a breakdown of value types found.
Duplicate keys matter — really?
Yes: JSON.parse silently keeps only the last one, which corrupts configs unpredictably across languages. Flagging duplicates catches real bugs early.
Is my data uploaded?
Never — validation is 100% client-side.
How do I fix invalid JSON quickly?
Start with the first reported position — later errors often disappear once it's fixed. The usual culprits: trailing commas, single quotes instead of double quotes, unquoted keys, and missing or extra commas between items.