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EVOA Toolbox

JSON Validator

Check whether JSON is valid and see the exact line and column of the first error, with a caret under the problem character.

Processed locally in your browser. Your text is not uploaded.

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What this tool does

Paste JSON and find out immediately whether it is valid. When it is not, you get the first error with its line and column, a plain-language explanation, and the offending line printed with a caret pointing at the exact character.

The checker is strict and follows the JSON specification, so it catches the mistakes that break real parsers: trailing commas, single quotes, unquoted property names, missing commas or colons, unclosed strings, bad escape sequences, leading zeros in numbers and stray text after the document.

Error positions come from a dedicated scanner rather than from a browser's error message, so the line and column are the same in Chrome, Firefox and Safari. Everything runs locally; your JSON is not uploaded.

How to use it

  1. 1Paste your JSON or upload a .json file.
  2. 2Look at the status: a green message means the document is valid.
  3. 3If it is invalid, read the message, then use the line, column and caret excerpt to find the problem.
  4. 4Fix it in the input box; the result updates as you type.

Supported formats

Strict JSON (RFC 8259). Comments, trailing commas, single quotes, NaN, Infinity and unquoted keys are reported as errors.

Privacy

This tool runs in your browser. The data you provide is processed on your device and is not sent to our servers.

Limitations

  • Only the first error is reported. After fixing it there may be more.
  • Validation checks syntax only, not whether the data matches a JSON Schema or your application's expectations.
  • Inputs over 5 MB are not validated automatically; you can opt in, but the page may be slow.
  • Columns count UTF-16 code units, so a line containing emoji may appear shifted by one per emoji compared with some editors.
  • Integers larger than 9,007,199,254,740,991 are valid JSON but will be rounded by JSON.parse in JavaScript; the validator warns you when it sees them.

FAQ

Why only one error at a time?

After a syntax error the rest of the text can no longer be interpreted reliably, so later “errors” are often just consequences of the first one. Fix the first, and the next one (if any) appears.

Does it validate against a schema?

No. It checks that the text is well-formed JSON. Schema validation (required fields, types, ranges) needs a JSON Schema validator.

Are comments allowed in JSON?

Not in standard JSON. Some tools (VS Code settings, tsconfig) accept comments, but APIs and JSON.parse do not. Remove comments before using the data elsewhere.

Is my data uploaded?

No, validation runs in your browser.

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