JSON Beautifier & Mock Data Generator

What this tool does

The JSON Beautifier checks JSON and lays it out with clear indentation and colors, or squeezes it onto one line (minify). It can also fill the box with sample API responses to practice on or test with.

How to use it

1. Paste your JSON into the left box.
2. Click Beautify to indent it (choose 2 spaces, 4 spaces or a tab), or Minify to remove every unneeded space.
3. If the JSON has a mistake, the tool shows what's wrong and where (line and column).
4. Click Copy to copy the result.

Your values stay exactly as typed

Many JSON tools read numbers as JavaScript numbers, which can only hold about 16 significant digits; anything above 9,007,199,254,740,991 gets rounded. A long ID like 12345678901234567890 would silently become 12345678901234567000. This tool checks your JSON, then only changes the spacing, so every number and string comes out exactly as you typed it.

Common JSON mistakes

• Trailing commas, like [1, 2, 3,], aren't allowed.
• Single quotes aren't allowed: strings and keys need double quotes.
• Unquoted keys, like {name: "Ana"}, are JavaScript, not JSON.
• Comments aren't part of JSON.
• Special values like undefined or NaN aren't allowed; use null.

A worked example

An API might send this reply on one line:

{"id":98765432109876543210,"user":"ana","tags":["new","vip"],"active":true}

Beautified with 2 spaces, it becomes:

{
              "id": 98765432109876543210,
              "user": "ana",
              "tags": [
                "new",
                "vip"
              ],
              "active": true
            }

The ID keeps all 20 digits. A tool that rebuilds the JSON from JavaScript numbers would print 98765432109876540000, which is a different user.

Frequently asked questions

Why is my API response one long line?

Servers usually send minified JSON to save bandwidth. Beautifying adds line breaks and indentation so people can read it; the data is the same.

Is it safe to paste API data here?

Yes. Everything runs in your browser and nothing is sent to a server. Still, avoid pasting live passwords or keys anywhere you don't need to.

What do the colors mean?

Keys, strings, numbers, true/false and null each get their own color, so you can scan the structure quickly.

Can JSON have comments or trailing commas?

Not standard JSON. Variants such as JSON5 and "JSON with comments" (used for some configuration files, like VS Code settings) allow them, but this tool checks standard JSON, so it will flag them as errors. Remove them first.

How big a file can it handle?

A few megabytes is fine on most computers. Very large files can make the page slow, because everything is processed in your browser's memory.

Related tools: Base64 Encoder / Decoder, URL Encoder / Decoder and Text Compare.

Sources: IETF, RFC 8259: The JSON Data Interchange Format (including its note on number precision); MDN Web Docs, Number.MAX_SAFE_INTEGER. JSON5, json5.org. Last reviewed on SuiteWebTools: October 2026.