JSON Formatter

{
  "name": "AEON Toolhub",
  "tools": 25,
  "free": true,
  "categories": [
    "productivity",
    "text",
    "developer"
  ],
  "owner": {
    "handle": "oiurireis"
  }
}

Why is my JSON invalid when it looks fine?

Usually because it was written the JavaScript or Python way. JSON is stricter than the code it came from, and five slips cause most of the errors:

• A trailing comma after the last item: [1, 2, 3,]
• Single quotes: 'name' instead of "name"
• Unquoted keys: {name: "Ana"}
• Comments, like // the brand, which JSON has no concept of
• Python values: True, False and None instead of true, false and null

The browser only reports a character offset, such as position 412, which is useless in a long file. This formatter turns it into a line and column, prints that line with a caret under the character, and says what is wrong in plain words. Click Try broken JSON to see it on this input:

{
  name: 'AEON Toolhub', // the brand
  tools: [1, 2, 3,],
  free: True,
}

The tool answers "Property names need double quotes" on line 2, column 3. Its Fix it button lists what it will change before you click it, here unquoted keys, single quotes, comments, trailing commas and Python values, and it only appears when the repaired text is valid JSON.

What does "Unexpected token < in JSON at position 0" mean?

It means the text is not JSON at all. A < at the very start is the beginning of an HTML page: the address you called returned a web page or an error page, such as a 404, a 502 or a login screen, instead of data. Paste it here and the tool says exactly that. Two close relatives:

• "Unexpected end of JSON input": the response was empty, or cut off before its last } or ].
• An unexpected token you cannot see at position 0: an invisible byte order mark, common in files saved by Windows programs. Fix it removes it.

Does formatting change your data?

Not here. A common way to build a formatter is to read the JSON into JavaScript values and write them back out, and JavaScript numbers are only exact up to 9,007,199,254,740,991. We pasted the same text into that approach and into this tool:

This formatter works from your text instead. It only changes spaces and line breaks, so 64-bit IDs, prices and escaped characters come out exactly as you pasted them. A key that appears twice in the same object is kept and marked as a duplicate under the output, because most parsers silently keep only the last one. Sort keys A-Z is the one option that moves anything: it reorders object keys, never values and never arrays.

Is it safe to paste API keys into an online JSON formatter?

It depends on where the formatting happens. In November 2025, security researchers at watchTowr reported more than 80,000 pastes exposed by two popular online formatters, including passwords, cloud keys and private keys. The cause was a save-and-share feature whose links could be guessed.

This formatter has no save or share feature and runs in your browser, so what you paste is not sent anywhere. You can check it yourself: open your browser's developer tools, go to the Network tab, paste your JSON, and no request leaves the page. For production secrets, the safest habit is still to swap real keys for placeholders before pasting them into any website.

When is a local tool better?

When the file is already on your machine, these do the same job without a browser tab:

• VS Code: run Format Document with Shift + Alt + F on Windows, Shift + Option + F on macOS, or Ctrl + Shift + I on Linux.
• jq: jq . data.json pretty-prints and jq -c . data.json minifies.
• Python: python -m json.tool data.json, with --sort-keys to order the keys.

A website wins when you only have the text, such as a response copied from logs or a chat, or when you want the error explained and fixed rather than just reported.

How much does minifying JSON save?

Less than most people expect on a flat file. In our test, minifying a GitHub API response indented with two spaces saved 10 to 12%, while a deeply nested package-lock.json saved 23%, since every level of nesting adds indentation to strip. From a four-space file the savings rise to 15 to 35%. The tool shows the exact figure for your file under the output, next to its size, key count and nesting depth. If the JSON travels over HTTP with gzip or Brotli, most of that whitespace is compressed away anyway, so minifying matters most where JSON is stored or logged as it is.