Guide
JSON Validator — complete guide
What does a JSON Validator check?
A JSON validator checks whether text follows the JSON grammar: matching braces, correctly quoted strings, legal commas, and allowed value types (object, array, string, number, boolean, null). It does not prove your business logic is correct — it proves the document can be parsed.
space4.dev’s JSON Validator highlights syntax problems with line and column context so you can fix broken API payloads before they hit production parsers.
How to validate JSON online
Follow these steps:
- Paste the JSON you want to check (or upload a .json file).
- Click Validate — or let the tool report status after you paste.
- If validation fails, read the error message and jump to the reported line/column.
- Fix quotes, commas, or brackets, then validate again until you see success.
- Copy the corrected JSON back into your editor, ticket, or API client.
Common JSON syntax errors
Most validation failures come from a short list of mistakes:
- Trailing commas after the last property in an object or array.
- Single quotes instead of double quotes around keys and strings.
- Unescaped control characters or broken Unicode escapes inside strings.
- Comments (// or /* */) — JSON does not allow comments.
- NaN, Infinity, or undefined — those are JavaScript values, not JSON.
Validate privately in the browser
Validation runs locally. You can safely check payloads that include auth headers, customer records, or staging secrets without uploading them to a third-party linting API.