What does "invalid JSON" mean?

JSON has strict syntax rules. Every key must be in double quotes, strings can't use single quotes, trailing commas after the last item are not allowed, and the structure must be properly closed with matching brackets and braces. When any of these rules are broken, the JSON is considered invalid and cannot be parsed by any standard parser.

What is the difference between formatting and minifying (compressing) JSON?

Formatting (pretty-printing) adds indentation and line breaks to make JSON human-readable — ideal for debugging or reviewing API responses. Minifying removes all unnecessary whitespace to reduce file size — ideal for sending JSON over a network or embedding it in code where readability doesn't matter. Both produce semantically identical data.

Why does a trailing comma cause a JSON error?

Unlike JavaScript, the JSON specification (RFC 8259) does not allow a comma after the last element of an object or array. For example, {"a":1,} and [1,2,3,] are valid JavaScript but invalid JSON. When you copy object or array literals from JS/TS code into a JSON file, trailing commas are a very common source of parse errors. This formatter will clearly report that error so you can fix it quickly.

JSON Formatter & Validator

Indent:

Input0 chars · 0 lines

Output

Result will appear here after you click Format or Minify.

About This Tool

Instantly format, pretty-print, or minify JSON. Catches syntax errors and highlights the exact line — no login, no uploads, all in your browser.

JSON (JavaScript Object Notation) is the most widely used format for API responses, configuration files, and data interchange. This formatter runs JSON.parse directly in your browser — your data never leaves your machine, making it safe to paste sensitive API responses or tokens.

How To Use

Paste your raw JSON into the Input area on the left.
Select Format to pretty-print, or Minify to compress.
When formatting, choose your preferred indentation width — 2 or 4 spaces.
Click the button and the result appears in the Output area on the right.
If the JSON has a syntax error, you'll see a clear error message and the line number when detectable.
Use Copy to copy the result to your clipboard, or Download .json to save it as a file.

Example

Valid JSON — before and after Format:

{"user":{"name":"Alice","age":30},"active":true}

{
  "user": {
    "name": "Alice",
    "age": 30
  },
  "active": true
}

Error example — trailing comma:

{"name": "Alice", "age": 30,}  ← trailing comma

A comma after the last item is not allowed by the JSON spec. This formatter will clearly identify the issue.

Frequently Asked Questions

What does "invalid JSON" mean?: JSON has strict syntax rules. Every key must be in double quotes, strings can't use single quotes, trailing commas after the last item are not allowed, and the structure must be properly closed with matching brackets and braces. When any of these rules are broken, the JSON is considered invalid and cannot be parsed by any standard parser.
What is the difference between formatting and minifying (compressing) JSON?: Formatting (pretty-printing) adds indentation and line breaks to make JSON human-readable — ideal for debugging or reviewing API responses. Minifying removes all unnecessary whitespace to reduce file size — ideal for sending JSON over a network or embedding it in code where readability doesn't matter. Both produce semantically identical data.
Why does a trailing comma cause a JSON error?: Unlike JavaScript, the JSON specification (RFC 8259) does not allow a comma after the last element of an object or array. For example, {"a":1,} and [1,2,3,] are valid JavaScript but invalid JSON. When you copy object or array literals from JS/TS code into a JSON file, trailing commas are a very common source of parse errors. This formatter will clearly report that error so you can fix it quickly.

This tool is provided for informational purposes only. Results are estimates and should not be relied upon as professional advice.

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