JSON Formatter

What this tool does

Paste JSON and this formatter re-indents it into something readable, tells you immediately whether it is valid, and — when it is not — points at the exact line and explains the problem in plain language rather than repeating your browser's error message.

It also minifies, sorts keys, shows a collapsible tree, and reports the document's size, key count and nesting depth. Everything runs in this tab, so it is safe to paste a production API response.

Common uses

• Making a single-line API response readable — log output and curl results almost never arrive formatted.
• Finding why a config file is rejected. The error location matters more than the error text, and a 4,000-character single line hides it completely.
• Sorting keys on two versions of a response so a diff shows real changes instead of reordered fields.
• Minifying before embedding JSON in an environment variable or a URL parameter.

A short example

This input:

{"user":{"id":7,"roles":["admin","editor"],"active":true}}

becomes:

{
  "user": {
    "id": 7,
    "roles": [
      "admin",
      "editor"
    ],
    "active": true
  }
}

Mistakes that break JSON

Four problems account for most invalid documents, and all four are things that would be perfectly legal in a JavaScript object literal:

• Trailing commas. {"a": 1,} is valid JavaScript and invalid JSON.
• Single quotes. JSON requires double quotes around both keys and string values.
• Unquoted keys. {a: 1} needs to be {"a": 1}.
• Raw newlines inside strings. They must be escaped as \n.

Comments are also invalid. If your config file has them, it is JSON5 or JSONC, not JSON — strip them before parsing with a standard parser.

Worth knowing

Formatting never changes your data, only whitespace. Key order is preserved unless you ask for sorting. One caveat applies to very large integers: JavaScript numbers lose precision above 2⁵³, so an ID like 9007199254740993 can come back altered. If your payload contains IDs that long, treat them as strings.