Online JSON Formatter
Instantly format, validate, and analyze your JSON payloads. ParseJSON provides a comprehensive suite of client-side developer tools—including a minifier, tree viewer, and diff checker—processing all data securely within your browser.
JSON Developer Tools
How to Format JSON
ParseJSON uses the native JSON.parse() and JSON.stringify() browser APIs — no third-party parsing library, no eval(). For files over 500KB, auto-format pauses to keep the editor responsive; just hit Format manually.
Common JSON Errors
Paste your JSON and hit Validate to get the exact line and column. Here are the most common mistakes:
{"a": 1 "b": 2}Add a comma after each value: {"a": 1, "b": 2}{"a": 1, "b": 2,}Remove the comma after the last item.{'key': 'value'}JSON requires double quotes: {"key": "value"}{key: "value"}Wrap keys in double quotes: {"key": "value"}{"a": 1 // comment}JSON does not support comments. Remove them.{"val": undefined}Use null instead. undefined and NaN are not JSON values.JSON Formatter Features
JSON vs JSON5
JSON5 is a superset of JSON designed to be easier to write by hand. It allows comments, trailing commas, single-quoted strings, unquoted keys, and hexadecimal numbers. However, JSON.parse() only handles standard JSON. If your file is a .json5 config (Babel, ESLint, etc.), you need a dedicated JSON5 parser. For API responses and data interchange, use standard JSON.
Frequently Asked Questions
How do I format JSON online?+
Paste your JSON into the input field, then click Format. ParseJSON will validate and prettify it with your chosen indentation (2, 3, 4 spaces, or tabs).
Is my JSON data safe?+
Yes. All JSON processing happens entirely in your browser using JavaScript. Nothing is sent to a server. Your data never leaves your machine.
Why is my JSON invalid?+
Common reasons include: missing commas between elements, keys not wrapped in double quotes, trailing commas after the last item, using single quotes instead of double quotes, unmatched braces or brackets, or using JavaScript values like undefined or NaN which are not valid JSON.
What is the difference between JSON and JSON5?+
JSON5 is a superset of JSON that allows comments, trailing commas, single-quoted strings, and unquoted keys. Standard JSON is stricter. JSON.parse() only handles standard JSON.
Can I format large JSON files?+
Yes. ParseJSON handles large files in the browser. For very large files (over 500KB), auto-format is disabled to keep the editor responsive. Use the Format button manually.
New to JSON?
Learn the syntax, data types, and common gotchas with our developer guides.