JSON Formatter & Validator
Format, validate, minify, and explore JSON — instantly, in your browser.
100% in your browser — files never leave your device
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What the JSON tool actually validates
Formatting, minifying, and validation all run through the browser's built-in JSON parser — no custom grammar, no partial-JSON tolerance. If your document isn't valid JSON, you get the parser's exact error message and the character position where it gave up, which is usually enough to find a stray trailing comma or unescaped quote.
The size comparison next to the indent selector is a real byte count, not an estimate — it measures the input and the minified output with the Blob API and shows the percentage saved. That number is what you'd actually save shipping minified JSON over the wire.
Tree view is convenient for exploring nested structures but re-renders the whole tree on every input change, so it can lag on documents in the tens-of-megabytes range. Switch to formatted or minified view for very large files — parsing and formatting stay fast even when the tree view doesn't.
Frequently asked questions
Is my JSON uploaded anywhere?
No. Parsing, formatting, and validation all happen in your browser with the native JSON engine. Nothing is sent to a server.
How big a file can it handle?
It handles multi-megabyte documents comfortably. Very large files (tens of MB) may be slow to render in tree view — use formatted or minified view instead.
What does the validator check?
It runs the standard JSON parser and reports the exact error message and position when the document is not valid JSON.