Does validation upload my file?
No. Parsing runs in the browser.
jfmt.dev
JSON Validator
Paste a payload to check that it is valid JSON. Errors stay in this tab — we do not send documents to a server.
JSON formatter
Input
Output · preview.json
{ }
Run a tool to see a polished result here
What validation checks
The validator parses the document as JSON. If it is valid you get a confirmation and a formatted view. If not, the editor reports the syntax problem. Use Repair when you pasted JavaScript-style JSON with comments or trailing commas.
Related tools
FAQ
Can it fix invalid JSON?
This page starts in validate. Switch to Repair in the sidebar to attempt automatic fixes.
Are duplicate keys reported?
Yes when the parser detects them. JSON officially allows only unique keys.