JSON Formatter & Validator

JSON & Data

Format, beautify, and validate JSON online with syntax error detection.

Indent

JSON Input

#json formatter#json beautifier#json validator#json pretty print#json lint

About JSON Formatter & Validator

Format, beautify, and validate JSON online with syntax error detection. JSON Formatter & Validator runs entirely in your browser — no installation, no uploads, and no data ever leaves your device.

Common use cases: debug malformed api responses; prettify minified config files; validate json before committing to version control. Whether you are debugging, prototyping, or building production code, having a fast and private tool for this task saves time compared to writing one-off scripts or using an online tool that logs your data.

Like every tool in Catalyst, this one is free forever, requires no login, and is safe to use with confidential data. All processing happens client-side via native browser APIs.

How to use JSON Formatter & Validator

1
Open the tool
Open JSON Formatter & Validator directly — no signup or installation required. The interactive interface loads instantly.
2
Paste or enter your input
Drop your data into the input area. The tool validates and processes your input live as you type or paste.
3
Review the result
The output updates instantly. If the tool has configuration options, adjust them and watch the result update.
4
Copy or download
Use the copy button to send the result to your clipboard. Nothing is saved between page loads, so closing the tab discards everything.

Frequently asked questions

What JSON errors does the validator catch?

It catches every RFC 8259 violation: missing or extra commas, unquoted keys, unterminated strings, invalid escape sequences, mismatched brackets, duplicate keys (warning), and non-standard values like NaN or undefined. Errors are shown with precise line and column numbers.

Can I change the indentation width?

Yes. The formatter supports 2-space, 4-space, and tab indentation. 2-space is the default and matches common style guides (Prettier, Google, Airbnb).

How large a JSON file can I format?

There's no hard limit. Most modern browsers comfortably handle JSON files up to 100–200 MB. For extremely large files, formatting happens in a single synchronous pass — you may see a brief pause while the browser parses and re-serializes the data.