JSON Validator & Formatter

Free Online JSON Formatter and Validator

JSON (JavaScript Object Notation) is the text format most APIs, configuration files and web apps use to exchange data. It is easy for programs to read, but a response from an API often arrives as one long unbroken line that no human can follow. This tool takes that raw text, checks that it is valid JSON, and either spreads it out into a readable layout or squeezes it down to its smallest size. Everything runs in your browser, so your data never leaves your device. If you are new to the topic, our guide What Is a JSON Formatter and Validator? explains the basics in more depth.

How to Use the JSON Formatter

1. Paste your JSON into the Input Raw JSON box.
2. Press Format (Pretty) to indent it so every object and array is easy to read, or press Minify to remove all extra spaces and line breaks.
3. If the text is not valid JSON, the tool reports an error instead of producing output. Fix the problem and try again (see the error table below).
4. Press Copy Output to copy the result, or Clear to start over.

Example: Before and After

Here is a small piece of JSON as many APIs return it, all on one line:

{"name":"Asha","age":29,"skills":["python","sql"],"address":{"city":"Berlin","zip":"10115"}}

After pressing Format (Pretty), the same data is laid out so the structure is obvious:

{
  "name": "Asha",
  "age": 29,
  "skills": [
    "python",
    "sql"
  ],
  "address": {
    "city": "Berlin",
    "zip": "10115"
  }
}

Nothing about the data changed. Only the spacing did. Pressing Minify turns it back into the single line.

Format or Minify: Which One Do You Need?

• Format (pretty print) when a person has to read the data: debugging an API response, reviewing a config file, checking a log entry or sharing an example in a bug report.
• Minify when a program is the reader: sending a request body, storing JSON in a database field, or embedding it in a URL or a script, where smaller text means less to transfer.

Common JSON Errors and How to Fix Them

Most invalid JSON comes from a small number of habits carried over from JavaScript code. JSON is stricter than a JavaScript object.

JSON Rules in Short

• A value is one of six things: text, a number, true or false, null, an object (curly braces) or an array (square brackets).
• Keys in an object are always text in double quotes.
• Items are separated by commas, with no comma after the last item.
• There are no comments and no functions. JSON is data only.
• The format is defined by RFC 8259 and is normally stored as UTF-8 text.

Limits to Know About

The formatter uses your browser’s own JSON parser, which is fast and reliable, but it has some side effects worth knowing:

• Very large whole numbers can lose precision. Numbers above 9007199254740991 cannot be stored exactly by JavaScript. An ID such as 9007199254740993 may come back slightly different. If your data has long IDs, keep them as text values.
• Duplicate keys collapse. If the same key appears twice in one object, only the last value is kept.
• Whole-number keys may move. Keys that look like whole numbers, such as “10” or “2”, can be listed before other keys in the output.
• It validates, it does not repair. The tool tells you whether the text is valid. It does not guess at fixes, because a wrong guess could silently change your data.
• It checks syntax, not meaning. Valid JSON can still have the wrong fields for your application. For that you need a schema check in your own code.
• Huge files depend on your device. Several megabytes is usually fine. Very large files can make the page slow because they are processed in your browser’s memory.

Privacy

Your JSON is parsed on your own device with the browser’s built-in JSON.parse function. The text is not uploaded, stored or logged, which makes the tool suitable for checking API responses and configuration files. As a general habit, still avoid pasting live passwords, private keys or tokens into any website.

Frequently Asked Questions (FAQ)

Is the JSON formatter free?

Yes. It is free, needs no sign-up and has no usage limit.

Is my JSON sent to a server?

No. The text is parsed in your browser using the built-in JSON.parse function and stays on your device.

What is the difference between formatting and minifying?

Formatting adds line breaks and indentation so people can read the data. Minifying removes them so the text is as short as possible. The data inside is identical either way.

Why does my JSON show an error?

The most common causes are a trailing comma, single quotes instead of double quotes, an unquoted key, a comment, or a missing bracket. The error table above lists each one with its fix.

Can JSON contain comments?

No. The JSON standard has no comment syntax. Some tools accept a relaxed variant called JSONC or JSON5, but ordinary JSON parsers reject comments, so remove them before sending data to an API.

Is JSON the same as a JavaScript object?

No. JSON looks similar, but it is stricter: keys and text must use double quotes, there are no trailing commas, and values such as undefined and functions are not allowed. JSON is text, while a JavaScript object lives in memory.

Does the tool fix invalid JSON for me?

No. It shows whether the input is valid and leaves the correction to you, so your data is never changed by guesswork.

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