Free online tool
JSON Formatter & Validator
Beautify, minify and validate JSON. Detailed error messages show you exactly where a problem lies.
Why formatted JSON matters
JSON is the lingua franca of modern APIs, config files, and data exchange between services. When it's minified, it's efficient over the wire but nearly impossible to read. When it's pretty-printed with indentation and line breaks, it becomes a document you can navigate, diff, and reason about. This tool switches between the two forms and, more importantly, tells you exactly where a syntax error lies so you can fix it fast.
How the validator works
The tool uses the browser's built-in JSON.parse, the same engine your Node.js server, your React app, and your browser DevTools rely on. That means the validation is authoritative — if it fails here, it will fail in your production code too. The error message includes the position of the first invalid token, which is usually a missing comma, an extra trailing comma, or a stray unescaped quote inside a string.
+Is my JSON uploaded anywhere?
No. Everything runs in your browser tab. Even a payload containing API keys or personal data is safe — nothing is transmitted.
+Does it support JSON5 or comments?
No. This tool follows strict RFC 8259 JSON, which does not allow comments or unquoted keys. Convert JSON5 to standard JSON first.
Making sense of JSON without leaving your tab
JSON looks simple until someone hands you a 40KB blob with no line breaks, mismatched brackets somewhere in the middle, and a trailing comma that your linter refuses to explain. A formatter turns that mess into an indented tree you can actually scan, and a validator tells you exactly where the parser gave up.
Most people reach for a formatter after copying a response straight out of a network tab or a log aggregator, where every API response arrives as one unbroken line. Reformatting it locally, without pasting it into a random website, also matters when the payload contains customer data, session tokens, or internal identifiers you'd rather not send to a third-party server.
Where the syntax actually breaks
JSON is stricter than JavaScript object literals: keys must be double-quoted strings, trailing commas are illegal, and comments have no place in the spec at all. A payload copied from a JS config file will often fail here for that reason alone, which is confusing the first time you see it since your editor's JS syntax highlighting made it look fine.
Single-quoted strings, unquoted keys, and NaN or undefined as values are all valid JavaScript but invalid JSON, and each produces a parse error at a specific character offset rather than a vague failure. Reading that offset carefully, and counting back to the nearest comma or brace, is usually faster than scanning the whole document by eye.
Minify versus pretty-print are different jobs
Pretty-printing adds indentation for humans; minifying strips every non-essential byte for transport. Neither changes the data structure, only its textual representation, so round-tripping through both should leave you with byte-identical parsed objects even though the strings look nothing alike.
Indentation width is a matter of preference, but two-space and four-space are the common conventions, and switching between them is purely cosmetic — no parser cares how many spaces precede a key, only that the brace and bracket nesting is consistent.
The gotcha with big numbers
JSON has no integer type distinct from float, and JavaScript's number type loses precision above 2^53. A 64-bit ID like a Snowflake or a database bigint can silently round when it passes through this or any browser-based formatter, so if you're inspecting IDs rather than just formatting layout, diff the raw string against the parsed output before trusting it.
Practical habit: paste untrusted API responses here first, before feeding them into your own code, so a malformed payload fails loudly in a throwaway tool instead of inside a stack trace three files deep in your app.
Escaped characters and Unicode inside strings
Control characters, quotes, and backslashes inside a JSON string must be escaped with a backslash, and non-ASCII characters can appear either as raw UTF-8 bytes or as \uXXXX escape sequences — both are valid and a formatter should render them identically once parsed. A string that looks like garbled boxes after formatting usually means the source encoding wasn't actually UTF-8 to begin with, not that the formatter mishandled it.
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