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Browser-Only JSON Validator
Strict JSON validation that never leaves your browser tab. Pinpoint errors with exact line and column numbers without sending a byte to any server.
Instant
Runs entirely in your browser — no upload, no wait.
100% private
Your JSON never leaves the tab. Nothing is logged.
No signup
Free, unlimited, no account required.
What "browser-only" actually means
All parsing, error detection, and reporting happens via JavaScript that the browser already loaded. There is no XHR or fetch call to a validation endpoint, no WebSocket, no analytics on the content. The DevTools network tab is the proof.
Validation rules
The validator implements RFC 8259: keys must be double-quoted strings, values must be one of the seven JSON types, no trailing commas, no comments, balanced braces, valid escape sequences, and well-formed Unicode.
Error reporting
Each error includes line, column, character offset, the offending token, and the recommended fix. Errors that share a root cause are grouped so you can fix them in one edit.
Line 5, col 14 — Unexpected ','. Trailing commas are not allowed by RFC 8259.
Line 7, col 3 — Unquoted key 'name'. JSON keys must be double-quoted strings.Why a separate tool from the formatter
A formatter rewrites your input. A validator only inspects it. For audit, compliance, or when you need to know whether a payload would parse without changing it, the validator-only path is what you want.
Privacy guarantees
Pure client-side. No upload, no logs, works offline once loaded.