JSON Validator Free Online

Free online JSON validator. Paste any JSON and instantly check for syntax errors with detailed error messages.

Formatted output...

Validation checks

  • Syntax correctness
  • Missing/extra commas
  • Unclosed brackets or strings
  • Root type detection (Object/Array)
  • Key and item count

A single character error in a JSON document - a misplaced comma, a missing quote, or an unescaped backslash - breaks the entire document and causes parsing failures. Tracking down these errors manually in large JSON files can take significant time. This free JSON validator identifies syntax errors instantly, shows you exactly where the problem is with line and character position information, and highlights the issue so you can fix it in seconds.

How to Use the JSON Validator

1

Paste your JSON

Paste the JSON you want to validate into the input area. The JSON can be minified (all on one line), pretty-printed with indentation, or partially malformed. The validator accepts any JSON regardless of its current formatting state - it validates the syntax directly without requiring any particular indentation style.

2

Check the validation result

The validator runs automatically as you type or paste. If the JSON is valid, you see a green "Valid JSON" indicator and the formatted output appears in the right panel. If the JSON contains a syntax error, a red error message appears showing the type of error, the line number, and the character position where the error was detected.

3

Fix errors and revalidate

Use the error location information to find and fix the issue in your JSON. After correcting the error, the validator immediately re-runs and shows the updated validation status. You can iterate on this fix-and-validate cycle until all syntax errors are resolved and you see the "Valid JSON" confirmation.

Common JSON Syntax Errors Detected

The validator checks for all syntax errors defined by the JSON specification (RFC 8259). The most common errors it catches are:

Trailing commas - a comma after the last element in an object or array is invalid JSON but valid JavaScript. This is the single most common JSON error, especially when copy-pasting from JavaScript object literals. Example: {"name": "John", "age": 30,} - the comma after 30 is the error.

Single quotes - JSON requires all strings (keys and values) to be enclosed in double quotes. Single quotes are not valid in JSON even though they are valid in JavaScript. {"name": 'John'} is invalid JSON - it must be {"name": "John"}.

Unquoted keys - JSON requires all object keys to be strings in double quotes. JavaScript object literal syntax allows unquoted keys, but JSON does not. {name: "John"} is invalid JSON - it must be {"name": "John"}.

Mismatched brackets - every opening { or [ must have a corresponding closing } or ]. A missing or extra bracket breaks JSON parsing. The validator identifies where the bracket mismatch occurs.

Unescaped special characters in strings - double quotes inside a string must be escaped as \". Backslashes must be escaped as \\. Newlines in strings must be represented as \n. Literal unescaped versions of these characters break JSON parsing.

Invalid number formats - JSON numbers cannot start with a leading zero (01234 is invalid - use 1234), cannot have a trailing decimal point (1. is invalid), and cannot be NaN or Infinity.

JSON Validator vs JSON Formatter

Both tools validate JSON, but they serve different primary purposes. The JSON Validator focuses specifically on identifying and explaining syntax errors - it is optimised for debugging malformed JSON and finding the exact location of problems. The JSON Formatter also validates JSON but focuses on presenting valid JSON in a readable, indented format with syntax highlighting. Use the validator when you have broken JSON you need to fix; use the formatter when you have valid JSON you want to read.

Frequently Asked Questions

What syntax errors does the JSON validator detect?
The validator checks for all JSON syntax errors including: trailing commas after the last element in objects or arrays, single quotes instead of double quotes, unquoted object keys, mismatched or missing brackets and braces, unclosed strings, invalid escape sequences within strings, invalid number formats (leading zeros, trailing decimals, NaN, Infinity), and any other character that violates the JSON specification (RFC 8259).
Does it show where the error is located?
Yes. When JSON is invalid, the error message includes the line number and character position where the parser encountered the error. For example: "Unexpected token , at line 5, column 18" tells you exactly where to look. Note that sometimes the reported location is where the parser noticed something was wrong, which may be slightly after the actual source of the error - the missing bracket may be reported at the closing location rather than where the opening was expected.
Does it also format valid JSON?
Yes. When your JSON is valid, the validator automatically displays the formatted, pretty-printed version with proper indentation. This makes it convenient to both validate and format in one step - paste your JSON, confirm it is valid, and copy the formatted version from the output panel.
Can it validate against a JSON Schema?
No. This tool validates JSON syntax only - it checks that the document is syntactically valid JSON that can be parsed. JSON Schema validation is a different and more advanced form of validation that checks whether the data structure matches a specific schema definition (required properties, data types, value ranges, etc.). For JSON Schema validation, you would need a specialised schema validation tool.
Is my JSON data secure during validation?
Yes. Validation runs entirely in your browser using JavaScript's native JSON.parse() function. Your JSON data never leaves your device and is never sent to any server. This makes the validator safe for validating sensitive data such as API configurations, authentication tokens embedded in JSON, database contents, and any proprietary data structures.