Paste your JSON below to format and validate it:
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Paste or drop .json
Formatted JSON will appear here…
Tip: Press Ctrl + Enter to format
Format, minify, and validate JSON with exact line and column errors.
Paste your JSON below to format and validate it:
Tip: Press Ctrl + Enter to format
Free online JSON formatter and validator. Paste JSON to beautify, minify, or check syntax — with precise error locations, duplicate-key warnings, and large-file support via Web Worker. Runs entirely in your browser; nothing is uploaded.
This online JSON formatter parses JSON with a hand-written, non-recursive parser instead of leaning entirely on the browser's built-in JSON.parse. That's what lets it point at the exact line and column of a syntax error — a missing comma, an unquoted key, a trailing comma before a closing brace — rather than showing you a generic "Unexpected token" message.
It also flags duplicate object keys, which valid-looking JSON can technically contain even though most systems (including JSON.parse) silently keep only the last one. If your document has {"id": 1, "id": 2}, you'll see a warning instead of quietly losing data.
Because the parsing and formatting happen in a Web Worker, pasting a multi-megabyte file won't freeze the page — the UI stays responsive while the worker does the heavy lifting on a separate thread. Extremely deeply nested documents (beyond 1,000 levels) are rejected with a clear message instead of crashing the tab with a stack overflow.
Use SparkJSON when you need a free JSON beautifier, validator, minifier, or viewer in one place — with no account wall and no upload of your payload.