MeridiaanJSON Validator and Formatter
Editor
Your JSON stays in your browser. It is never uploaded and nobody reads it.
Result
Nothing to check yet
Paste JSON on the left, open a file or try an example.
How to use it.
- 1
Paste your JSON.
Type or paste into the left panel, or open a .json file. Checking starts as you type.
- 2
Read the result.
A valid document shows its size and what it contains. An invalid one shows the line and column of the first error, with the line itself and a hint when the mistake is a common one.
- 3
Take it away.
Copy the formatted or minified result, download it as a file, or send it back to the editor.
What gets checked.
Strict JSON.
The checker follows the JSON standard, RFC 8259: double-quoted strings and keys, no trailing commas, no comments, and only true, false and null as words. Single quotes, undefined, NaN and Python’s None are flagged with a note on how to fix them.
Your data stays as written.
Formatting changes only whitespace. 1.0 stays 1.0, 1e2 stays 1e2, a 20-digit integer keeps all its digits and keys keep their order unless you ask to sort them. A tool that parses and prints your JSON again rewrites those numbers without telling you.
Duplicate keys.
A key that appears twice in the same object is valid JSON, and JavaScript keeps only the last value. The checker lists each duplicate with its line so none slips by.
Private by design.
Everything runs in your browser. The text you paste is never sent to a server.
Questions.
Is my JSON uploaded anywhere?
No. Checking, formatting and minifying all run in your browser, and the text you paste never leaves your device.
What does a JSON validator check?
Whether the text follows the JSON syntax: matched braces and brackets, double-quoted keys and strings, commas between items and none after the last, valid numbers and valid escape sequences. It reports the first error with its line and column.
Why does my JSON fail because of a trailing comma?
JSON does not allow a comma after the last item of an object or an array, although JavaScript does. Remove the comma and the document validates.
Can it read comments or single-quoted strings?
No, standard JSON has neither. The checker points at them so you can remove them or switch to double quotes. JSON5 and JSONC are different formats.
What is the difference between formatting and minifying?
Formatting adds line breaks and indentation so people can read the document. Minifying removes every space outside strings so the document takes the fewest bytes.
Why check JSON that an Agent wrote?
Agents return JSON for tool calls, configuration files and structured output, and one stray comma or comment makes the program that reads it fail. Paste the output here to find the exact spot.
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