JSON Formatter and Validator Online: Format, Beautify, Minify (Free)

Paste your broken JSON above and click Validate to see the exact error with line and column numbers. This tool finds and helps you fix the most common JSON syntax errors instantly.

Common JSON Errors and How to Fix Them

1. "Unexpected token" or "SyntaxError: JSON.parse"

This is the most common JSON error. It usually means:

• Trailing comma: {"name": "John", "age": 30,} - remove the comma after the last value.
• Single quotes instead of double quotes: {'name': 'John'} - JSON requires double quotes: {"name": "John"}.
• Unquoted keys: {name: "John"} - keys must be in double quotes: {"name": "John"}.
• Comments in JSON: {"name": "John" // user name} - JSON does not support comments. Remove them or switch to YAML.

2. "Unexpected end of JSON input"

Your JSON is incomplete. Common causes:

• Missing closing bracket ] or brace }
• Truncated response from an API (check network tab)
• Empty string passed to JSON.parse("")

3. "Expected property name or '}'"

There is a structural error, usually a missing comma between key-value pairs:

// Wrong - missing comma
{"name": "John" "age": 30}

// Correct
{"name": "John", "age": 30}

4. "Unexpected number / string"

Usually means a missing colon between key and value, or a value where a key is expected.

JSON Formatter for Large Files

This formatter handles large JSON files (up to 50MB) directly in your browser. Unlike server-based formatters, your data stays on your device - ideal for formatting large API responses, database exports, or log files containing sensitive data. The tool uses JavaScript's native JSON.parse() which is highly optimized in modern browsers.

JSON Beautifier vs Minifier

The beautifier (Format button) adds 2-space indentation and line breaks for readability. Use it when inspecting API responses, debugging webhooks, or reviewing configs. The minifier removes all whitespace to produce the smallest possible output. Use it when sending JSON over the network, storing in databases, or embedding in code.

JSON Validator with Error Messages

The validator checks if your JSON is valid according to the JSON specification (RFC 8259). When errors are found, it shows the exact error message with the line number and column, so you can jump straight to the problem. This is especially useful for large files where finding a misplaced comma manually would take hours.

Syntax Highlighting and Tree View

The syntax-highlighted output color-codes strings, numbers, booleans, null values, and keys for easy visual parsing. The tree view presents your JSON as a collapsible hierarchy - perfect for navigating deeply nested API responses or complex configuration objects.

100% Client-Side - Your Data Never Leaves Your Browser

This tool runs entirely in your browser. No data is sent to any server. This makes it safe to format JSON containing API keys, credentials, personal data, or proprietary business logic. For additional security, you can encrypt sensitive text or share it via a zero knowledge encrypted paste.

Related Tools

• JSON Schema Validator - validate JSON against a JSON Schema definition
• JSON to YAML Converter - convert between JSON and YAML formats
• CSV to JSON Converter - convert CSV files to JSON arrays
• XML to JSON Converter - convert XML documents to JSON
• Diff Checker - compare two JSON files side by side
• JSON Formatting Best Practices - naming conventions, nesting depth, and common mistakes
• YAML vs JSON Comparison - which format to use and when

How do I fix invalid JSON online?

Paste your JSON into the editor above and click "Validate." The tool will show the exact error message with the line number and column where the problem is. Common fixes include: adding missing commas between values, replacing single quotes with double quotes, removing trailing commas, and removing comments (JSON does not support comments).

What does "Unexpected token" mean in JSON?

This error means the JSON parser encountered a character it did not expect at that position. The most common causes are: trailing commas after the last element ({"a":1,}), single quotes instead of double quotes, unquoted property names, or JavaScript comments in JSON data. Paste your JSON above to find the exact position.

Can I format large JSON files online?

Yes. This tool handles JSON files up to 50MB directly in your browser. Since all processing happens client side using the browser's native JSON parser, large files are processed quickly without uploading anything to a server.

Is my JSON data safe when using this tool?

Yes. This JSON formatter runs 100% in your browser. No data is transmitted to any server. You can verify this by checking the Network tab in your browser's DevTools - no requests are made when you format or validate JSON.

What is the difference between JSON.parse() errors in different browsers?

Chrome and Edge show errors like "Unexpected token X in JSON at position N." Firefox shows "JSON.parse: expected property name or '}'" with a line number. Safari shows "JSON Parse error: Expected '}'." This tool normalizes these errors and always shows the line and column number regardless of browser.

Why does my API response fail with "JSON parse error"?

Common reasons: the server returned HTML instead of JSON (check if the Content-Type header is application/json), the response was truncated (check Content-Length), the response contains a BOM (byte order mark) before the JSON, or the server returned an error page (like 500 or 403). Paste the raw response above to diagnose the exact issue.

How do I validate JSON without escaping special characters?

Paste your JSON directly into the editor. This tool handles all valid JSON including strings with escaped characters (\", \\, \n, \t, \u0000). If your JSON contains literal backslashes, they must be escaped as \\ in the JSON string.