JSON Validator
Validate JSON strings against RFC 4627 in strict or lenient mode — pinpoint syntax errors, structural issues, and type mismatches instantly.
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What to expect
Built for developers
Strict mode follows the RFC exactly. Lenient mode accepts common JSON relaxations like trailing commas and single-quoted strings.
Runs client-side. Your data never leaves your browser.
No ads, no trackers, no popups. Pure focus.
Paste code or upload files. Both modes supported.
Share output with teammates via a permanent link.
Adapts to your system preference automatically.
Fully responsive. Works on any screen size.
More tools coming
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OpenFormatter is launching with 30+ tools on day one.
About this tool
OpenFormatter's JSON Validator checks JSON against RFC 4627 (The application/json media type for JavaScript Object Notation) and the JavaScript language specification. Supports both strict and lenient validation modes. Reports exact line and column numbers for errors. Works with files up to several megabytes. Paste or upload your JSON — validation happens instantly client-side.