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jsonblocks

Free online JSON formatter

Paste minified or messy JSON and get clean, indented output locally. This free JSON formatter validates as you type, explains errors in plain language, and runs entirely in your browser - your data never leaves the page.

Input

Valid JSON · 160 B

Formatted

224 B
{
  "app": "jsonblocks",
  "version": 2.4,
  "darkMode": true,
  "retired": null,
  "owner": {
    "name": "Ada Lovelace",
    "id": 1024,
    "verified": true
  },
  "tags": [
    "json",
    "viewer",
    "formatter"
  ]
}

Formatting only adds whitespace - your data stays byte-identical. Everything runs locally; nothing is uploaded.

How to format JSON with jsonblocks

  1. Paste your JSON into the input panel or load the sample.

  2. Pick 2-space or 4-space indentation for the output.

  3. Read the formatted result on the right; invalid JSON shows exactly what broke.

  4. Copy the formatted output back to your editor, API client, or bug report.

Frequently asked questions

What does a JSON formatter do?

A JSON formatter (also called a JSON beautifier or pretty-printer) takes compact JSON and reprints it with line breaks and indentation so the structure is easy to read. It never changes your data - only the whitespace.

Will formatting change my data?

The formatter parses and serializes the document. It adds indentation, but number representations and key ordering can change, and unsafe large integers may lose precision. Keep the original text when exact bytes or numeric precision matters.

Should I use 2-space or 4-space indentation?

Either is valid JSON. Two spaces is the most common convention for config files and API payloads; four spaces can read better for deeply nested documents. Pick whichever your project already uses.

Why does my JSON fail to format?

A formatter can only print valid JSON. The usual culprits are trailing commas, single quotes instead of double quotes, unquoted keys, and comments. The validator on this page points at the exact line and column.

Is there a size limit?

There is no fixed limit. Small documents format locally; very large pastes stay on the fast synchronous path up to hundreds of kilobytes, and the main viewer handles multi-megabyte files in a background worker.

What is the difference between a formatter, a beautifier, and a validator?

Formatter and beautifier are the same thing: pretty-printing. A validator checks whether JSON is syntactically correct and reports errors. This page does both - it formats valid input and explains invalid input.