JSON Formatter & Validator

JSON Formatter & Validator - Pretty Print and Validate JSON Online

Format & Validate JSON

Our tool serves two essential functions for anyone working with JSON. The formatter takes messy or minified JSON and makes it readable with clean indentation and line breaks. This is often called "pretty printing." The validator checks your code against JSON grammar rules to instantly find errors, showing you exactly what needs to be fixed. It's perfect for debugging API responses or ensuring your data structures are sound.

How to Use This JSON Formatter

We designed our tool to be fast and straightforward, helping you get clean, valid JSON in just a few clicks.

1. Format and Validate: The tool automatically checks the syntax and formats the code.
2. Copy the result: Grab the clean, well-formed JSON from the output field to use in your application.

What Counts as "Valid JSON"

JSON (JavaScript Object Notation) has a strict set of rules that our validator checks against. If your data doesn't follow these rules, it can cause errors in your applications.

Here are the key requirements for valid JSON:

• Data Types: Supports objects, arrays, strings, numbers, booleans (true/false), and null.
• Lowercase Literals: The values true, false, and null must be in lowercase.
• Double Quotes: All property keys and string values must be enclosed in double quotes ("). Single quotes are not allowed.
• No Trailing Commas: A comma cannot be the last item in an object or array.
• Numbers: Numbers cannot have leading zeros (e.g., 012 is invalid). Special values like Infinity or NaN are also not permitted.
• Unique Keys: While some parsers might accept duplicate keys in an object, the JSON standard advises against it. The behavior is unpredictable, as the last key will often overwrite all previous ones.

Formatter vs. Validator

It's helpful to understand the different roles our tool plays:

• Validator (JSON Lint): This function acts like a grammar checker for your code. It answers the question, "Is this JSON text well-formed and syntactically correct?" It finds issues like missing brackets or invalid commas.
• Formatter (Beautifier): This function focuses on readability. It takes valid JSON and adds indentation and line breaks to make it easy for humans to read, without changing the data itself.

Examples

See how our tool can instantly clean up and fix common JSON issues.

Minified to Pretty-Printed:

• Before:

  {"id":1,"name":"John Doe","isActive":true,"roles":["admin","editor"]}

• After:

  {
    "id": 1,
    "name": "John Doe",
    "isActive": true,
    "roles": [
      "admin",
      "editor"
    ]
  }

Invalid JSON and Fixes:

• Trailing Comma: {"key": "value",} -> Our validator will flag the final comma.
• Single Quotes: {'key': 'value'} -> Keys and strings must use double quotes: {"key": "value"}.

Troubleshooting

When JSON fails to parse, it's almost always due to a small syntax error. Here are the most common problems we see:

• Trailing Commas: The most frequent error. Make sure no comma appears after the last element in an object or array.
• Incorrect Quotes: Remember, JSON requires double quotes for all keys and string values. Single quotes from JavaScript objects will cause an error.
• Comments: Standard JSON does not support comments. If you paste code with // or /* */ comments, it will be flagged as invalid.
• Duplicate Keys: If you have two keys with the same name in an object, the last one usually wins. This can lead to unexpected data loss, so our tool warns you about it.

Frequently Asked Questions

What is a JSON formatter?

A JSON formatter, or "pretty printer," is a tool that adds indentation and line breaks to raw JSON data. It makes the code structured and easy for people to read without changing the underlying data.

What is a JSON validator / JSON lint?

A JSON validator checks if your code adheres to the strict syntax rules of the JSON format. It's like a spell-checker for your data, catching errors like trailing commas, missing quotes, or mismatched brackets.

Does pretty printing change the JSON data?

No. Formatting only changes the whitespace (spaces, tabs, line breaks) to improve readability. The actual data - the keys and values - remains exactly the same.

Why are trailing commas invalid in JSON?

The original JSON specification did not allow for trailing commas to ensure maximum compatibility across different programming languages and parsers. While some JavaScript environments permit them, they are a common source of errors in strict JSON contexts.

Why do keys/strings need double quotes in JSON?

This rule simplifies the parsing process and eliminates ambiguity. Unlike JavaScript objects where quotes can sometimes be optional for keys, JSON's strict requirement for double quotes ensures data is interpreted consistently everywhere.

Are duplicate keys allowed in JSON objects?

The JSON standard states that keys within an object SHOULD be unique. While many parsers will technically accept duplicates, they will often silently overwrite previous values, leading to unpredictable behavior and data loss.

What indentation should I use (2 vs. 4 spaces vs. tabs)?

This is purely a matter of personal or team preference. Two spaces is the most common convention you'll see in the wild, as it keeps the file compact while still being readable.

Is my JSON processed locally in the browser or uploaded to a server?

Your privacy is our priority. All formatting and validation happen directly in your browser. Your data is never sent to, or stored on, our servers.