Tulnest

JSON Formatter & Validator

Paste JSON and instantly format, validate and minify it. Errors show the exact line and column. Works fully offline in your browser.

Input0 chars
Output
0 chars
Formatted JSON will appear here.

Paste JSON into the input, choose an indent style, and get back a pretty-printed (or minified) version. If the JSON is invalid, you'll see the exact line and column where parsing failed — handy when tracking down stray commas or missing quotes.

Parsing is done with the browser's built-in JSON.parse — the same implementation your app's runtime uses — so what validates here will validate in production. Your data never leaves the page.

How to use

  1. Paste JSON into the Input pane. If you want something to play with first, click Load sample.
  2. Pick an indent: 2 spaces, 4 spaces, tab, or minify (no whitespace for compact output).
  3. Formatted output appears on the right. If the JSON is invalid, you'll see a red error box showing the exact line and column where parsing failed.
  4. Click Copy to copy the formatted output to your clipboard.

Frequently asked questions

What's the difference between formatting and validating?
Formatting re-indents your JSON so it's easy to read. Validating checks that the text is syntactically correct JSON. This tool does both at once — if your JSON is invalid, you'll see a precise error message instead of formatted output.
Does this tool send my JSON anywhere?
No. Parsing and formatting happen entirely in your browser. Safe to paste sensitive data.
What indent sizes are supported?
2 spaces, 4 spaces, tabs, or minify (no whitespace). The default is 2 spaces, which matches most style guides.

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