Free Online JSON Formatter
Format, validate, and beautify your JSON data instantly with our free online JSON formatter.
Unlike other tools, formatting happens in real-time as you type — no button clicks needed.
When your JSON has errors, you get plain-English explanations with exact line and column numbers
so you can fix issues fast.
Features
- Real-time formatting — JSON is formatted as you paste or type, with a 300ms debounce for smooth performance
- Smart error messages — Instead of "Unexpected token," see "Missing comma after property on line 12"
- Syntax highlighting — Color-coded keys, strings, numbers, booleans, and null values
- Collapsible tree view — Explore nested JSON structures by expanding and collapsing nodes
- Minify & prettify — Switch between compact (minified) and readable (prettified) output
- Configurable indentation — Choose 2 spaces, 4 spaces, or tabs
- Dark mode — Developer-friendly dark theme by default, with light mode toggle
- One-click copy — Copy formatted output to clipboard instantly
- 100% client-side — Your data never leaves your browser. No server processing.
- Mobile responsive — Works on phones and tablets
What is JSON?
JSON (JavaScript Object Notation) is a lightweight data format used to exchange data between servers and web
applications. It's human-readable, easy for machines to parse, and has become the standard format for APIs,
configuration files, and data storage.
A valid JSON document must start with either an object {} or an array []. All property
names must be double-quoted strings, and values can be strings, numbers, booleans, null, objects, or arrays.
Common JSON Errors
Trailing Commas
JSON does not allow trailing commas after the last element in an object or array. This is valid in JavaScript but
invalid in JSON:
{ "name": "John", "age": 30, } ← trailing comma is invalid
Single Quotes
JSON requires double quotes for strings. Single quotes are not valid:
{ 'name': 'John' } ← must use double quotes: { "name": "John" }
Unquoted Keys
All property names in JSON must be wrapped in double quotes:
{ name: "John" } ← invalid: must be { "name": "John" }
Missing Commas
Each key-value pair must be separated by a comma:
{
"name": "John"
"age": 30 ← missing comma after "John"
}
How to Use This JSON Formatter
- Paste your JSON into the input panel on the left (or top on mobile)
- See instant results — formatted output appears automatically in the right panel
- Fix errors — if your JSON is invalid, check the error message for the exact issue
- Adjust settings — change indentation, switch to minified mode, or explore the tree view
- Copy the result — click the Copy button to grab the formatted JSON
Frequently Asked Questions
Is my data safe?
Yes. All formatting happens entirely in your browser using JavaScript. Your JSON data is never
sent to any server. This tool works offline too.
What's the maximum JSON size I can format?
There's no hard limit. The tool handles files up to several megabytes smoothly. Very large files
(10MB+) may cause brief pauses during formatting.
What's the difference between JSON Formatter and JSON Validator?
A JSON formatter takes valid JSON and makes it readable (adding indentation and line breaks).
A JSON validator checks whether your JSON is syntactically correct. This tool does both simultaneously.
Can I minify JSON?
Yes. Click the "Minify" button in the controls bar to compress your JSON by removing all
whitespace. This is useful for reducing file size in production.
What browsers are supported?
All modern browsers: Chrome, Firefox, Safari, Edge, and their mobile versions. No plugins or
extensions required.