JSON Formatter & Validator

Valid JSON follows a strict grammar: object keys must be double-quoted strings, string values must use double quotes (not single), trailing commas after the last item are not allowed, and only six value types exist — string, number, boolean, null, object, and array. JavaScript is more permissive than JSON; code that works as a JS object literal often isn't valid JSON.

The most common causes: single quotes instead of double quotes around strings or keys, a trailing comma after the last item in an object or array, an unquoted key, or a stray comment (JSON doesn't support comments at all, unlike JSON5 or JSONC). This tool's error message includes the position where parsing failed, which is usually right at or just after the actual problem.

Formatting (pretty-printing) adds indentation and line breaks so JSON is readable by a human — useful when debugging or reviewing an API response. Minifying strips all unnecessary whitespace to produce the smallest possible size — useful for production payloads or storing JSON in a constrained space, since whitespace has zero effect on how JSON parsers interpret the data.

No — parsing, formatting, and validation all happen using JSON.parse() and JSON.stringify() directly in your browser via JavaScript. Nothing is uploaded or transmitted, which matters if you're working with real API responses or data that might contain sensitive information.

It can handle typical API responses and config files without issue, but extremely large payloads (multiple megabytes) may feel sluggish since the whole string is parsed and re-rendered in the browser at once. For very large files, a command-line tool like jq is usually a better fit than a browser-based formatter.