What is JSON Formatter?
JSON Formatter and Validator is a free browser-based developer tool that pretty-prints minified JSON, validates syntax and helps debug malformed JSON data. Paste raw or minified JSON and click Format to instantly indent it with proper nesting, making the structure readable without writing any code.
JSON (JavaScript Object Notation) is the dominant data interchange format used by REST APIs, configuration files, databases and web applications. Minified JSON removes all whitespace to reduce file size, but makes it unreadable to humans during development and debugging. The formatter adds consistent two-space indentation, line breaks and color-coded key/value pairs.
The validator checks for common JSON errors: unquoted keys, trailing commas (allowed in JavaScript but not in JSON), mismatched brackets, invalid escape sequences in strings, and incorrect value types. When an error is found, the exact line and character position is reported so you can fix it immediately. The Minify function compresses formatted JSON back to a single line for production use or API requests.
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How to use JSON Formatter
- Paste your JSON data into the input box — minified or raw
- Click Format to instantly pretty-print with proper indentation
- Use Validate to check for syntax errors — exact error location is shown
- Copy the formatted JSON or use Minify to compress it back
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Frequently asked questions
What is the difference between format and minify?
Formatting (pretty-printing) adds consistent indentation and line breaks to make JSON human-readable. Minification removes all unnecessary whitespace to produce the smallest possible file. Both contain exactly the same data — only the whitespace differs. Use formatted JSON for development and debugging; use minified JSON for production payloads and configuration files where file size matters.
What is JSON validation?
JSON validation checks that the text conforms to the JSON specification (RFC 8259). Valid JSON must use double-quoted strings, has no trailing commas, no comments, and uses only the six data types: string, number, boolean (true/false), null, object, and array. The validator parses the text and reports the exact line and character position of any syntax error.
Can I validate JSON Schema?
JSON Schema validation (checking that JSON data matches a schema definition) is different from syntax validation. This tool validates JSON syntax — that the text is well-formed JSON. For JSON Schema validation, dedicated tools like AJV (Node.js) or online schema validators are appropriate.
Why does my JSON have a "trailing comma" error?
JSON (unlike JavaScript) does not allow a comma after the last item in an object or array. Remove the comma on the last key-value pair or last array element. If you are generating JSON programmatically, use JSON.stringify() in JavaScript or the json module in Python — both produce valid JSON automatically without trailing commas.
How do I handle JSON with comments?
Standard JSON does not support comments. If you have a configuration file with comments (common in .jsonc files or build tool configs), strip the comments before parsing. You can use the find-and-replace to remove // comment lines, or use a JSONC parser that natively supports comments. The formatter can handle JSONC if you strip comments first.
What indentation size should I use?
Two spaces is the most common convention for JSON in web development contexts (API responses, config files, package.json). Four spaces is common in Python projects. For compressed storage and transmission, zero spaces (minified). All are equivalent in terms of the data they represent. Choose based on your team or project convention.
Can I format very large JSON files?
Yes. The tool runs in your browser with no server involved, so processing is limited only by your device memory. For files above a few MB, consider using command-line tools like jq for better performance: jq . data.json > formatted.json. For files in the hundreds of MB range, browser-based tools may be slow and command-line is strongly recommended.
What is the difference between JSON and JSON5?
JSON5 is a superset of JSON that allows JavaScript-style extensions: comments, trailing commas, single-quoted strings, unquoted keys, and hexadecimal numbers. JSON5 is valid in tools that explicitly support it but is not valid standard JSON. Most APIs and configuration parsers expect standard JSON. JSON5 is mainly used in human-edited configuration files where the authoring convenience matters.
Can I convert JSON to CSV or other formats?
JSON-to-CSV conversion requires a flat or flattened data structure and is not built into this formatter. For JSON-to-CSV, many online converters and command-line tools (jq with @csv filter, Python pandas) handle it well. JSON can also be converted to YAML, XML, or other formats through dedicated conversion tools.
Why does valid-looking JSON fail validation?
The most common causes are: a BOM (byte order mark) at the start of the file (invisible in most editors), a non-standard encoding character, Unicode control characters embedded in string values, or the text being JSONL (JSON Lines — one JSON object per line) rather than a single JSON value. Try removing the first character if validation fails on what looks like valid JSON.
- API response debugging: Paste a raw API response to format it into readable indented JSON for inspection. Most REST APIs return minified JSON that is impossible to read without formatting.
- Configuration file editing: Many tools (Prettier, ESLint, package.json, tsconfig.json) use JSON config files. Validate before saving to catch syntax errors that would silently break the tool.
- Data transformation preparation: Format JSON before writing transformation scripts so you can clearly see the data structure, keys, and nesting.
- Minification for production: Remove all whitespace before embedding JSON in HTML or sending in an API request to reduce payload size.
- Comparison: Format two JSON blobs with consistent indentation before diffing them to see only meaningful data changes, not formatting differences.
JSON in Practice — Developer Use Cases
- Trailing commas:
{"key": "value",}— The last item in an object or array cannot have a trailing comma. Valid in JavaScript but not in JSON. - Single quotes:
{'key': 'value'}— JSON requires double quotes for all strings and keys. Single quotes are not valid. - Unquoted keys:
{key: "value"}— All keys must be quoted strings. Unquoted keys are valid JavaScript object notation but not JSON. - Missing commas between items:
["a" "b" "c"]— Items in arrays and objects must be separated by commas. - Comments:
// This is a comment— JSON does not support comments. Use JSONC (JSON with Comments) or strip comments before parsing. - Undefined or NaN values: JSON supports null, true, false, numbers, strings, objects, and arrays only.
undefinedandNaNare not valid JSON values.
JSON has strict syntax rules. These are the most frequent errors the validator catches:
Common JSON Errors and How to Fix Them
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Last updated: April 11, 2026
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