What's the difference between a validator and a parser?

Functionally similar — both verify JSON syntax — but a validator focuses on reporting whether JSON is valid and where it's wrong, while a parser produces a usable data structure. This tool does both: it parses your JSON, and uses the parser's success or failure to determine validity, surfacing detailed error messages when the parser fails.

What kinds of errors does the validator catch?

All RFC 8259 violations: unquoted keys (use "key" not key), single-quoted strings (use "value" not 'value'), trailing commas in arrays or objects, comments (JSON has no comment syntax), missing closing brackets/braces, control characters in strings, malformed Unicode escapes, and stray characters outside the root value. Each error reports the exact line and column where it occurred.

Does the validator check schema or just syntax?

This tool validates JSON syntax only — whether your input is well-formed JSON. It does not check JSON Schema (whether the data matches a particular structure with required fields, types, and constraints). For schema validation, use a JSON Schema validator with a schema file describing your expected shape.

Why does the validator say my JSON5 / JSONC is invalid?

JSON5 (which allows comments, single quotes, and trailing commas) and JSONC (JSON with comments, used in tsconfig.json) are NOT standard JSON. This validator enforces strict RFC 8259, which rejects all of those features. To validate JSON5/JSONC files, first strip the non-standard syntax with a converter, or use a JSON5-aware validator.

Can I validate a large JSON file?

Yes. Validation happens in your browser via JSON.parse, which handles files up to ~50 MB quickly. Larger files (hundreds of MB) may take seconds and use significant memory. For multi-gigabyte JSON, consider streaming validators like jq or specialized libraries that don't load the entire document into memory.

How accurate is the line/column error reporting?

Very accurate. The error position is computed from the byte offset in your input — same source the JSON parser uses. Line numbers are 1-indexed, columns are 1-indexed character positions within the line. The reported location points to the first character that violated the spec — fixing it usually requires looking just before that position.

Is my data sent anywhere?

No. Validation happens entirely in your browser using the native JSON.parse API. Your data never leaves your device — safe for confidential payloads, internal config, or any JSON containing PII or sensitive information.

JSON Validator

Validate JSON syntax online with detailed error messages and line numbers. Free JSON validator for debugging malformed JSON data.

Data / JSON JSON Tools

Instant results

JSON Input

Formatted JSON

About JSON Validator

Validate and format JSON data. This tool checks for syntax errors, reports the error location, and can format your JSON with proper indentation. It also shows statistics about your JSON structure.

How to Use JSON Validator

Paste your JSON

Paste your JSON into the input editor on the left. Validation runs automatically as you type — no submit button needed.

Read the validation result

A green badge with 'Valid JSON' appears for well-formed input; a red badge with 'Invalid JSON' shows the exact error message and line/column position when something's wrong.

Inspect the formatted output (if valid)

When your JSON is valid, the right panel shows it with proper indentation. Useful for visually confirming the structure matches your intent and for spotting unexpected nesting or values.

Fix and re-validate

If invalid, fix the highlighted location and re-validation happens instantly. Common fixes: add missing closing brackets, remove trailing commas, change single quotes to double quotes, or quote unquoted keys.

When to Use JSON Validator

Pre-commit JSON validation

Before committing a config file, API mock, fixture, or any JSON to version control, paste it here to catch syntax errors that would break consumers. A few seconds of validation prevents production incidents from malformed JSON deployed via CI/CD pipelines.

Debugging API integration errors

When an API client returns 'JSON parse error' but doesn't show details, capture the raw response (browser DevTools → Network tab → Response → Copy) and paste it here. The line/column error report tells you exactly which character broke parsing — often a stray newline, BOM, or HTML error page wrapped around expected JSON.

Validating user-submitted JSON

Building an app where users paste JSON (config editor, query builder, data importer)? Test edge cases here first: empty objects, deeply nested structures, escape sequences, large numbers, Unicode characters. Confirm the inputs you accept produce the expected validation outcome before shipping.

Verifying generated JSON output

If your app produces JSON programmatically (template strings, manual concatenation, or low-level serialization), validate sample outputs here to catch bugs early. Especially valuable for code that doesn't use a robust JSON library — common in shell scripts, embedded systems, and manual logging.

JSON Validator Examples

Valid JSON passes

Input

{
  "name": "Alice",
  "age": 30,
  "skills": ["JS", "TS", "React"]
}

Output

Valid JSON

All quotes are double-quoted, all keys are strings, the trailing closing brace matches the opening, no trailing commas, no comments. The validator parses it successfully and shows the formatted output alongside structure stats (characters, minified size, depth).

Trailing comma triggers error

Input

{
  "name": "Alice",
  "age": 30,
}

Output

Invalid JSON: Unexpected token } in JSON at position 33 (Line 4, Column 1)

The trailing comma after '30' is illegal in standard JSON (though valid in JavaScript and JSON5). The validator pinpoints the exact line and column — line 4, column 1 — where the parser hit the unexpected closing brace. Remove the comma after '30' to fix.

Unquoted key fails validation

Input

{ name: "Alice", age: 30 }

Output

Invalid JSON: Unexpected token n in JSON at position 2

Object keys must be wrapped in double quotes in JSON (unlike JavaScript object literals where unquoted keys are allowed). The validator reports the issue at position 2, where 'name' starts without quotes. Fix: change to {"name": "Alice", "age": 30}.

Tips & Best Practices for JSON Validator

1.Always validate JSON received from external sources (APIs, file uploads, user input) before processing it. Even well-known APIs occasionally return HTML error pages disguised as JSON during outages — validation catches these before they break your application.
2.When debugging, validate the EXACT bytes from the source. Copy-pasting JSON through email, Slack, or markdown editors can introduce smart quotes ("), zero-width characters, or BOMs that visually look fine but break parsing. Use 'view source' or curl to capture raw output.
3.Line/column numbers are 1-indexed (line 1, column 1 = first character). Most code editors use the same convention, so you can navigate directly to the error using your editor's 'Go to line' feature (Ctrl+G in VS Code, Cmd+L in Sublime).
4.If you see 'Unexpected end of JSON input', your input is truncated — likely missing a closing bracket or brace. Count opening { and [ characters and ensure each has a corresponding closing pair. Or check whether the source actually delivered a complete response.
5.JSON forbids comments. If you have a config file with // or /* */ comments, you need JSONC (JSON with Comments) or JSON5 — both supported by tools like VS Code, but require pre-processing before standard JSON parsers like this validator can handle them.
6.For schema validation (checking that required fields exist with correct types, not just syntax), use a separate JSON Schema validator. This tool only verifies syntactic correctness — a syntactically valid JSON document might still fail your application's schema requirements.

Frequently Asked Questions

A JSON validator parses your input against the JSON specification (RFC 8259) to verify it's syntactically correct. It checks that every bracket and brace is balanced, every string is properly quoted with double quotes, every key has a value, types are valid (string, number, boolean, null, object, array), and there are no trailing commas or comments. If anything is invalid, you get the exact error position.

JSON Validator

About JSON Validator

How to Use JSON Validator

Paste your JSON

Read the validation result

Inspect the formatted output (if valid)

Fix and re-validate

When to Use JSON Validator

Pre-commit JSON validation

Debugging API integration errors

Validating user-submitted JSON

Verifying generated JSON output

JSON Validator Examples

Valid JSON passes

Trailing comma triggers error

Unquoted key fails validation

Tips & Best Practices for JSON Validator

Frequently Asked Questions

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