Paste JSON to format, validate, minify, or sort keys — all in-browser, nothing sent to a server
JSON Formatter and Validator parses, validates, and prettifies JSON data with configurable indentation. Paste any JSON — API responses, configuration files, package.json, or clipboard data — and the tool instantly formats it with proper indentation, highlights syntax errors with line numbers, and shows the data tree. It also minifies JSON (removes all whitespace) for production use.
JSON (JavaScript Object Notation) is the universal data interchange format for web APIs, configuration files, and data storage. Valid JSON has strict rules: strings must use double quotes (not single), keys must be quoted strings, trailing commas are not allowed, and undefined and functions are not valid values. A single syntax error makes the entire document invalid — this tool pinpoints exactly which line and character caused the error.
Beyond formatting, this tool provides a collapsible tree view of nested objects and arrays, making it easy to navigate large API responses without losing track of structure. You can collapse deeply nested sections and expand only the parts you need. The tree view also shows the data type of each value (string, number, boolean, null, array, object).
API response with nested objects
Result: {"user":{"id":1,"name":"Alice","address":{"city":"NYC","zip":"10001"}}} → prettified with 2-space indentation and collapsible tree
Find a JSON syntax error
Result: {'key': 'value'} — immediately shows error 'Unexpected token' because single quotes are not valid JSON; must be double quotes
Minify a config file
Result: { "debug": false, "port": 3000 } → {"debug":false,"port":3000} — 40% smaller for production
What is the difference between JSON and JavaScript objects?
JavaScript object literals allow single quotes, unquoted keys, trailing commas, comments, and undefined/function values. JSON requires double-quoted keys and string values, disallows trailing commas, and only allows string, number, boolean, null, array, and object types. JSON is a strict data interchange format; JavaScript object literal notation is more permissive.
Why does JSON not allow trailing commas?
JSON was designed to be a strict, unambiguous format for any programming language to parse. Trailing commas (like [1,2,3,]) are valid in JavaScript but cause parse errors in strict parsers. JSON5 is an extension that allows trailing commas, comments, and single quotes — but it is not standard JSON and requires a special parser.
What is the maximum size of JSON this tool can handle?
The tool handles JSON up to several MB in the browser. Very large JSON (50MB+) may cause browser slowdowns. For large datasets, consider using command-line tools: python -m json.tool or jq (a powerful JSON processor) for better performance.
How do I convert JSON to a CSV or spreadsheet?
Use the CSV to JSON converter tool in reverse, or copy the JSON array and use an online JSON-to-CSV converter. For complex nested JSON, you may need to flatten it first — choose which nested keys to promote to columns.
What is the JSON5 format?
JSON5 is a superset of JSON that allows JavaScript-style syntax: single-quoted strings, unquoted keys, trailing commas, comments (// and /* */), hexadecimal numbers, and multiline strings. It is more readable for configuration files but requires a JSON5 parser. Standard JSON parsers reject JSON5 syntax.