JSON Formatter & Validator

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Parsing happens in your browser with the JavaScript engine's own JSON parser. That matters more than it sounds: most online JSON formatters POST your payload to a server, and JSON being debugged is very often a real API response with real customer data, tokens or internal hostnames in it. Paste that into a random site and you have made a disclosure.

You can verify the claim — disconnect from the network and this page keeps working.

Reading the error message

When JSON is invalid, we give you the line and column and print the surrounding lines with a caret under the offending character. Nine times out of ten it is one of four things:

• A trailing comma. Legal in JavaScript, illegal in JSON. The most common cause by a wide margin.
• Single quotes. JSON requires double quotes on both keys and string values.
• Unquoted keys. {name: "x"} is a JavaScript object literal, not JSON.
• An unescaped character in a string — a raw newline, tab, or backslash. Windows paths are a frequent offender: C:\Users needs to be C:\\Users.

Comments are also invalid in strict JSON, whatever your editor lets you get away with. JSONC and JSON5 are different formats.

What the stats tell you

Key count, array count and maximum nesting depth are useful when you are deciding whether a payload is reasonable. Deep nesting — past five or six levels — usually means the shape is fighting you, and it makes every consumer of that API harder to write. Null count is worth a glance too: a field that is null in every record is often a field that was never wired up.