JSON is a common format for storing and exchanging structured data. You can format and validate it without writing code by using a JSON formatter and validator, a browser developer tool, or a no-code data tool.

Formatting makes JSON easier to read by adding indentation and line breaks. Validation checks whether the JSON follows the correct syntax and structure.

Understand What JSON Looks Like

JSON uses key-value pairs, arrays, objects, numbers, strings, booleans, and null values.

{
  "name": "Alex Morgan",
  "age": 29,
  "isActive": true,
  "skills": ["writing", "editing", "research"],
  "address": {
    "city": "Manchester",
    "country": "United Kingdom"
  }
}

Common JSON data types include:

JSON requires double quotation marks around keys and string values. Single quotation marks are not valid in standard JSON.

Format JSON With an Online Formatter

An online JSON formatter is the simplest option for most people.

1. Copy your JSON data.
2. Open an online JSON formatter or validator.
3. Paste the JSON into the input area.
4. Click Format, Beautify, or Prettify.
5. Review the formatted result.
6. Copy the formatted JSON back into your file, app, or API request.

Formatting adds spacing and indentation, turning this:

{"name":"Alex","age":29,"active":true}

into this:

{
  "name": "Alex",
  "age": 29,
  "active": true
}

Both versions contain the same data, but the formatted version is much easier to read and edit.

Validate JSON Syntax

Validation checks whether the JSON is structurally correct. A validator will usually point to the line or character where it finds a problem.

Common JSON errors include:

How to validate JSON

1. Paste your JSON into a formatter or validator.
2. Click Validate, Check JSON, or Format.
3. Read the error message if validation fails.
4. Go to the indicated line or nearby section.
5. Fix the issue.
6. Validate again until the tool confirms the JSON is valid.

A formatter may refuse to format invalid JSON. In that case, fix the syntax error first.

Use Browser Developer Tools

Modern web browsers include developer tools that can format and inspect JSON returned by a website or API.

In Chrome or Edge

1. Open the page or API response containing JSON.
2. Press F12 to open developer tools.
3. Go to the Network tab.
4. Reload the page or trigger the request.
5. Select the relevant request.
6. Open the Response or Preview tab.
7. Review the formatted JSON data.

This is useful when you need to inspect data from a web application without copying it into another tool.

Format JSON in a Text Editor

Many text editors include JSON formatting through built-in features or extensions.

VS Code

1. Open the JSON file.
2. Select all text with Ctrl + A on Windows or Command + A on Mac.
3. Open the command palette with Ctrl + Shift + P or Command + Shift + P.
4. Type Format Document.
5. Select it to format the file.

VS Code can also highlight syntax errors as you type. If it does not format the file, check for a JSON syntax error or confirm the file is saved with a .json extension.

Validate JSON Structure, Not Just Syntax

A JSON validator can confirm that the text is valid JSON, but it may not know whether the data has the fields your app expects.

For example, this is valid JSON:

{
  "customer": "Alex",
  "total": 25
}

But an application expecting customerName and orderTotal may reject it because the field names do not match.

To validate structure, check:

• Required fields are present
• Field names match exactly, including capitalization
• Values use the expected type
• Arrays contain the expected kind of items
• Nested objects have the required properties
• Dates, IDs, and numbers follow the expected format

If you are working with an API, use its documentation or schema to confirm the required structure.

Clean Up JSON Data

After formatting, review the data for common issues.

• Remove duplicate keys if your use case does not allow them
• Check for accidental spaces in field names
• Confirm numbers are not wrapped in quotation marks unless they should be text
• Check that true and false are lowercase
• Confirm null is lowercase
• Remove trailing commas
• Ensure all brackets and braces are closed
• Check that special characters are properly escaped

For example, this is invalid because True is capitalized:

{
  "active": True
}

The correct version is:

{
  "active": true
}

Work With Large JSON Files

For large files, avoid pasting sensitive or very large JSON into an online tool unless you are comfortable with its privacy policy.

Instead:

1. Open the file in a code editor such as VS Code.
2. Use the editor’s formatting command.
3. Use the editor’s search function to find specific keys.
4. Collapse sections to navigate large nested objects.
5. Save a backup before making major edits.

For very large JSON files, a desktop editor or command-line JSON tool is usually more reliable than a browser-based formatter.

Common JSON Mistakes

Using JavaScript object syntax

JavaScript allows unquoted keys and single quotes in many cases, but standard JSON does not.

Invalid JSON:

{
  name: 'Alex',
  age: 29
}

Valid JSON:

{
  "name": "Alex",
  "age": 29
}

Leaving a trailing comma

JSON does not allow a comma after the final item.

Invalid:

{
  "items": ["a", "b", "c",]
}

Valid:

{
  "items": ["a", "b", "c"]
}

Mixing brackets and braces

Use curly braces {} for objects and square brackets [] for arrays.

{
  "tags": ["json", "data"],
  "author": {
    "name": "Alex"
  }
}

Including comments

Standard JSON does not support comments. Remove // or /* */ comments before validating.

Quick Workflow

1. Copy the JSON data.
2. Paste it into a JSON formatter or validator.
3. Fix any syntax errors the validator identifies.
4. Format the JSON for readability.
5. Check field names, data types, and required fields.
6. Save a backup of the original file.
7. Copy the validated JSON into your app, API request, or configuration file.

Use an online formatter for quick tasks, a code editor for larger files, and a validator to catch syntax errors. Formatting makes JSON readable, while validation confirms it can be parsed correctly—then check the structure against the requirements of the app or API that will use it.