How to Format and Validate JSON Data Step by Step
Quick Answer
To format JSON: paste your JSON into the JSON Formatter, and the beautified output with proper indentation appears instantly. To validate JSON: the tool automatically checks syntax and shows an error with location if invalid. All processing happens locally — your data is never uploaded.
Introduction
JSON (JavaScript Object Notation) is the most common data format for web APIs and configuration files. Raw JSON from APIs is often minified into a single line, making it hard to read. Formatting (also called beautifying or pretty-printing) adds indentation and line breaks so humans can read it. Validation checks that the JSON syntax is correct — a single misplaced comma or missing quote can break your entire application. This guide shows you how to format and validate JSON in your browser.
Step by Step
-
Open the JSON Formatter tool
Go to the JSON Formatter tool page. The tool accepts any JSON string as input — objects, arrays, or nested structures.
-
Paste your JSON data
Paste the JSON you want to format or validate into the input textarea. This could be an API response, a config file, or a JSON string from your code.
-
Review the formatted output
The tool parses your JSON and re-serializes it with 2-space indentation and line breaks. The formatted output appears instantly in the result field. If the JSON is invalid, an error message appears with the location of the syntax problem.
-
Check validation status
If the JSON is valid, the tool shows a success indicator and the formatted output. If invalid, it displays the parse error — such as 'Unexpected token at position 42' — so you can fix the syntax issue in your source.
-
Copy or minify the result
Use the Copy button to copy the formatted JSON to your clipboard. Some tools also offer a Minify button to remove all whitespace — useful for reducing payload size in production.
Examples
Format minified JSON
Input: {"name":"Alice","age":30,"roles":["admin","user"]}
Output: {
"name": "Alice",
"age": 30,
"roles": ["admin", "user"]
}
Detect invalid JSON (trailing comma)
Input: {"a":1,"b":2,}
Output: Error: Unexpected token } at position 11
Detect invalid JSON (single quotes)
Input: {'name':'Alice'}
Output: Error: Unexpected token ' at position 1
Common Problems
- Using single quotes for strings —JSON requires double quotes for all strings and keys.
- Trailing commas after the last item —JSON does not allow a comma before } or ].
- Comments in JSON —standard JSON does not support // or /* */ comments. Use JSONC or JSON5 if you need comments.
- Unquoted keys —unlike JavaScript object literals, JSON requires all keys to be in double quotes.
- Undefined, NaN, or Infinity values —JSON only supports null, not undefined or NaN.
Tips
- Always validate JSON before sending it in an API request —a syntax error can cause a 400 Bad Request response.
- Use minified JSON in production to save bandwidth, and formatted JSON in development for readability.
- JSON does not support Date objects —serialize dates as ISO 8601 strings (e.g., "2026-09-02T00:00:00Z").
- Use JSON.parse() in JavaScript to convert a JSON string to an object, and JSON.stringify() to convert an object to a JSON string.