What are the most common JSON syntax errors?

The most frequent issues are: trailing commas after the last item in an array or object, single quotes instead of double quotes around keys or strings, missing commas between items, and unescaped special characters inside strings.

Does the validator check the data schema, not just syntax?

The validator checks JSON syntax (well-formedness) only. Schema validation — verifying that required fields are present and have correct types — is a separate step typically done against a JSON Schema document.

Why does my JSON pass validation but my app still rejects it?

Your app may be enforcing a schema on top of valid JSON syntax. Check for missing required fields, wrong data types (e.g., a number where a string is expected), or values outside an allowed range.

Validate JSON Syntax Online

A single misplaced comma, an unmatched bracket, or a trailing comma can break JSON parsing entirely — and tracking down the offending character in a large payload can take far longer than it should. devtoolkit.sh's JSON Validator checks your JSON against the official RFC specification and reports exactly where the syntax error is, including the line number and column offset, so you can jump straight to the problem. This is especially valuable when working with hand-edited configuration files, template outputs, or data that has been through multiple transformations. After fixing syntax errors, the JSON Formatter can also visually confirm the structure looks correct by rendering it with proper indentation. Use the validator as a quick sanity check before sending data to an API, storing it in a database, or committing a configuration file to version control. Everything runs in your browser — no uploads, no waiting, no data retention.

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FAQ

What are the most common JSON syntax errors?: The most frequent issues are: trailing commas after the last item in an array or object, single quotes instead of double quotes around keys or strings, missing commas between items, and unescaped special characters inside strings.
Does the validator check the data schema, not just syntax?: The validator checks JSON syntax (well-formedness) only. Schema validation — verifying that required fields are present and have correct types — is a separate step typically done against a JSON Schema document.
Why does my JSON pass validation but my app still rejects it?: Your app may be enforcing a schema on top of valid JSON syntax. Check for missing required fields, wrong data types (e.g., a number where a string is expected), or values outside an allowed range.