DevToolbox

JSON Formatter & Validator

JSON (JavaScript Object Notation) is the most common data format used by web APIs, configuration files, and modern applications. This JSON formatter lets you paste minified or messy JSON and instantly turn it into a clean, indented, human-readable structure. It also validates your JSON as you go, pointing out exactly where a syntax error occurs so you can fix it quickly instead of hunting through a wall of text.

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Your data stays in your browser — this tool runs entirely on the client side and nothing is uploaded to a server.

How to Use the JSON Formatter & Validator

  1. Paste or type your JSON into the input box.
  2. Click "Format" to beautify it with proper indentation, or "Minify" to compress it onto one line.
  3. If the JSON is invalid, an error message will show what is wrong and roughly where.
  4. Use "Copy" to copy the result, or "Download" to save it as a .json file.

What is JSON?

JSON is a lightweight, text-based data format built on two structures: objects (key-value pairs wrapped in curly braces) and arrays (ordered lists wrapped in square brackets). It is language-independent but uses conventions familiar to programmers using C-family languages, which is a big reason it became the default format for REST APIs, configuration files, and data interchange between systems.

Why use a JSON formatter?

APIs and databases frequently return JSON as a single unbroken line to save bandwidth. That is efficient for machines but nearly unreadable for humans. Formatting adds consistent indentation and line breaks so you can visually scan the structure, spot the field you are looking for, and understand how objects and arrays are nested inside one another — which is especially useful while debugging.

Common JSON errors

The most frequent mistakes are: trailing commas after the last item in an object or array (not allowed in JSON, unlike JavaScript objects), using single quotes instead of double quotes for strings and keys, missing commas between items, mismatched or unclosed brackets/braces, and using the value undefined, which is valid in JavaScript but not valid JSON.

Example

Minified input
{"name":"Ada","skills":["math","programming"],"active":true}
{
  "name": "Ada",
  "skills": [
    "math",
    "programming"
  ],
  "active": true
}

Tips

  • Keys and string values must always use double quotes, not single quotes.
  • Numbers, booleans (true/false), and null are written without quotes.
  • JSON does not support comments — strip them before validating.
  • Use minify before sending JSON over a network to reduce payload size.

Frequently Asked Questions

Is JSON case-sensitive?

Yes. Keys like "Name" and "name" are treated as completely different properties, and reserved values (true, false, null) must be lowercase.

Can JSON contain comments?

No. The JSON specification does not support comments of any kind. If you need annotated configuration, consider JSON5, YAML, or a JSON file with a separate documentation file.

Is my JSON uploaded anywhere?

No. Formatting and validation run entirely in your browser using standard JavaScript — your data is never sent to a server.

Why does my JSON fail to parse even though it looks correct?

The most common invisible culprit is a trailing comma or a smart/curly quote character pasted in from a word processor instead of a straight double quote.

Related Tools

JSON Minifier Compress JSON by removing whitespace and line breaks. JSON to CSV Converter Convert a JSON array of objects into a CSV file. CSV to JSON Converter Convert CSV data into a JSON array of objects. YAML to JSON Converter Convert YAML configuration into JSON format. XML to JSON Converter Convert XML documents into JSON format.