JSON Validator
Paste, upload, or drop a JSON file and see instantly whether it's valid. Errors are flagged inline with the exact line and column as you type — no guessing which bracket or comma broke your document.
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What this JSON validator checks
Valid JSON follows a strict, unambiguous spec (RFC 8259): object keys and strings must be double-quoted, arrays and objects must have matched brackets, and there's no room for trailing commas or comments — rules that make JSON predictable for every parser, in every language. This validator enforces exactly that spec, so anything that passes here will also parse cleanly with Python'sjson module, JavaScript'sJSON.parse, or any other language's JSON parser.
Instead of a vague "unexpected token" message, the hand-written parser behind this tool reports the exact line and column where parsing failed, and separately warns about duplicate object keys — valid per the spec, but almost always an accident worth catching before it ships. Validation runs continuously as you type, upload, or drop a file, and large documents are checked in a background Web Worker so the page never freezes.
Once your JSON is valid, the same workspace lets you format it, minify it, browse it as a tree, or convert it live to XML,YAML, orCSV — no separate tool required.
Does this check JSON automatically, or do I have to click a button?
Automatically — every keystroke, paste, or file drop is re-validated as you type, with any error underlined right where it happens. The "Validate JSON" action in the Actions panel also runs an explicit check and shows a toast confirming the result, useful when you just want a clear yes/no without scanning the editor.
What exactly does this validator check?
Strict JSON syntax per RFC 8259: matched brackets and braces, double-quoted keys and strings, no trailing commas, no comments, and only the value types JSON actually allows (string, number, boolean, null, object, array). It also separately flags duplicate object keys as a warning, since duplicate keys are technically parseable (the last one wins) but almost always a mistake.
Where does it show the error location?
Directly in the status line below the toolbar — "Line X, col Y" — and the editor underlines the offending token, so you can jump straight to the problem instead of scanning the whole document for a stray comma or missing quote.
Can it validate large JSON files without freezing the page?
Yes. Parsing and validation run in a background Web Worker, so a multi-megabyte file is checked without blocking the editor or the rest of the page.