JSON Formatter & Validator

JSON (JavaScript Object Notation) is a lightweight, text-based data interchange format. It is easy for humans to read and write, and easy for machines to parse and generate. JSON is built on two structures: a collection of name/value pairs (objects, written as {"key": "value"}) and an ordered list of values (arrays, written as [1, 2, 3]). Despite its name, JSON is language-independent and is used by virtually every programming language and platform.

A JSON formatter (also called a JSON pretty printer) takes compact or irregularly indented JSON and rewrites it with consistent indentation — typically 2 or 4 spaces per level. The result shows each key-value pair on its own line with nested structures visually indented, making the hierarchy immediately readable. Formatted JSON is functionally identical to the original — only whitespace is added.

No. All formatting, validation, and minification happens entirely in your browser using the JavaScript JSON.parse() and JSON.stringify() APIs. Your JSON data is never sent to any server, never logged, and never stored anywhere outside your own browser tab. You can verify this by opening your browser's Network tab in developer tools while using the tool — you will see no outgoing requests.

Paste your JSON into the input area and click Validate JSON. The tool attempts to parse the text and reports whether it is structurally valid. If invalid, it shows the error message along with the approximate line and column number where parsing failed. You can also use Format JSON — if it succeeds, the JSON is valid. The tool also runs live validation as you type, updating the status indicator automatically.

JSON minification removes all unnecessary whitespace — spaces, tabs, and newlines — from JSON text without changing its data. Minified JSON is functionally identical to formatted JSON but takes fewer bytes, reducing file size and speeding up data transfer over networks. It is commonly used in production API responses and when embedding JSON in HTML documents where every byte matters.

The most common causes of invalid JSON are:

• Trailing commas — {"a": 1,} is invalid JSON (valid in JavaScript)
• Single quotes — JSON requires double quotes for all strings and keys
• Unquoted keys — {a: 1} is not valid JSON
• Comments — JSON does not support // or /* */ comments
• Mismatched brackets — unclosed {, [, or "
• Missing commas — between items in an array or object
• Invalid values — undefined, NaN, and Infinity are not valid JSON

JSON parsing errors occur when the text does not conform to the JSON specification. The error message will name the unexpected token and its position. Common messages:

• Unexpected token } in JSON at position N — often a trailing comma
• Unexpected token ' in JSON at position N — single-quoted string
• Unexpected token u in JSON at position N — undefined value
• Unexpected end of JSON input — missing closing bracket or quote

Yes. Files up to a few megabytes format instantly. Very large files (tens of megabytes) may take a few seconds and could temporarily slow the page. The tool has no file size limit, but browser memory constrains practical use. For files over 10 MB, command-line tools are more efficient:

• jq . file.json — using the jq command-line tool
• python -m json.tool file.json — using Python's built-in module
• cat file.json | python3 -m json.tool — pipe version

No. Formatting only adds whitespace — it does not change keys, values, types, or structure. Minification also preserves all data. The only edge case is that JSON.parse and JSON.stringify may normalize certain JavaScript behaviors, such as rounding floating-point numbers with excessive precision or reordering object keys in some engines. For standard JSON data, all values will be preserved exactly.

Yes, completely free. No sign-up, no account, no API key, no rate limits, and no data is ever sent to any server. It is a free public utility provided by SwissArmyTechTools for developers, IT admins, sysadmins, and anyone who works with JSON.

Yes. Click Format JSON — if the JSON is invalid, the tool first attempts a safe, automatic repair before formatting. It can remove leading, trailing, and dangling commas, convert smart/curly quotes and single-quoted strings or keys to standard double quotes, strip JavaScript-style comments, add double quotes around unquoted property names, remove extra closing }/], add missing closing }/], strip a UTF-8 byte order mark (BOM), and trim stray whitespace. If a repair is applied, the result is pretty-printed and a summary of what was fixed is shown above the editor. The tool only applies a fix if the result is valid JSON afterward — it never guesses at missing commas or values, since that could change the meaning of your data. If the JSON cannot be safely repaired, your input is preserved and the tool highlights the exact line and column of the problem with a plain-English explanation.