UFOZoo

JSON Formatter — Beautify, Validate & Minify JSON Online

Format, minify, pretty-print, and syntax-highlight JSON data. Features key sorting, custom indentation, tree view, error highlighting, and file upload.

Features

  • ✓Real-time JSON formatting as you type — paste and it formats instantly
  • ✓Syntax highlighting with color-coded keys (purple), strings (green), numbers (blue), booleans (amber), and nulls (red)
  • ✓Collapsible tree view for exploring nested JSON structures at any depth
  • ✓Instant validation with precise error location — highlights the exact line number in red when JSON is invalid
  • ✓Key sorting — alphabetize object keys for consistent output across environments
  • ✓Custom indentation — choose 2 spaces, 4 spaces, or tab to match your project's style guide
  • ✓Line numbers displayed by default for easy reference when debugging or comparing diffs
  • ✓One-click minify to compress JSON for production APIs or reduce payload size
  • ✓Drag-and-drop files or click to browse — supports any .json file
  • ✓One-click copy to clipboard for easy sharing and pasting into other applications
  • ✓Download formatted output as .json file or copy to clipboard in one click
  • ✓Entirely client-side — zero data transmission, works offline after initial load

How to Use

  1. 1Paste JSON into the left editor — it formats automatically as you type. Or drag a .json file onto the page.
  2. 2Switch between Formatted view (pretty-printed), Tree view (collapsible nodes), and Minified (compressed) using the tabs.
  3. 3Click the indent buttons (2 / 4 / Tab) to change spacing. Toggle Sort Keys to alphabetize object keys.
  4. 4When validation fails, the error line number turns red in the left panel — click it to jump to the problem.
  5. 5Click Copy or Download on the right toolbar to save your formatted JSON.
  6. 6In Tree view, click the triangle arrows to expand or collapse nested objects and arrays for easier exploration.
  7. 7Use the Upload button to open a .json file from your device instead of pasting manually.
  8. 8Toggle the Minified tab to compress JSON for production — great for reducing API payload size.
  9. 9Use the Copy button to grab the output in any view mode — formatted, tree, or minified.

Frequently Asked Questions

What is JSON formatting?

∨
JSON formatting (also called beautifying or pretty-printing) adds proper indentation and line breaks to compact JSON data. This makes it readable, easier to debug, and simpler to edit. Most APIs return minified JSON to save bandwidth — this tool reverses that so you can actually read it.

Is my data sent to a server?

∨
No. Every operation happens entirely in your browser using JavaScript. Your JSON data never leaves your device, is never transmitted over the network, and is never stored anywhere. You can even disconnect from the internet after the page loads and it will still work.

What does the error line highlight mean?

∨
When you paste invalid JSON (missing comma, trailing comma, unquoted key, etc.), the validator detects the exact position of the error. The corresponding line number in the left panel turns red, and the error message below shows the line number and column position so you can fix it quickly.

What's the difference between Format and Minify?

∨
Format (or beautify) expands JSON with indentation and newlines for readability — use this for debugging, editing, or documentation. Minify removes all whitespace to produce the smallest possible output — use this for API responses, reducing file size, or embedding JSON in HTML attributes where space matters.

Does it support comments or trailing commas?

∨
No. Strict JSON (RFC 8259) does not allow comments (// or /* */) or trailing commas. If your input contains these, the validator will report an error. For JSONC (JSON with comments), consider stripping comments before pasting, or use a JSONC-specific parser.

How do I copy the formatted JSON?

∨
Click the Copy button on the right toolbar to copy the entire formatted output to your clipboard. You can also click Download to save it as a .json file.

Is there a file size limit?

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The practical limit depends on your device's available memory. Most files under 5-10 MB work smoothly in modern browsers. Extremely large files (50+ MB) may cause sluggishness due to browser rendering limits. For those cases, use a command-line tool like `jq` or Python's `json.tool` module instead.

Can I use this on mobile?

∨
Yes. The layout automatically adapts to smaller screens — input and output panels stack vertically on mobile devices. All features including formatting, tree view, copy, and download work on touch screens. Drag-and-drop upload also works on mobile browsers that support the File API.

How do I copy just a portion of a large JSON?

∨
In Tree view, right-click (or long-press on mobile) on any node to copy only that sub-tree. In Formatted view, select the exact text you want with your cursor, then copy normally. The toolbar Copy button always copies the full output. For large files, consider using Tree view to navigate to the relevant section first.

What is 'Sort Keys' and when should I use it?

∨
Sort Keys alphabetizes all object keys in the JSON output. Use it when: (1) comparing two JSON files side by side — sorted keys make diffs cleaner, (2) generating consistent output for version control to prevent false diffs, (3) when your team's coding standards require alphabetical key ordering. Note: JSON arrays maintain their original order.

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