JSON Formatter

Format, indent, or minify JSON online. 100 % local processing in your browser: no data is sent to a server.

Indentation

2 spaces

4 spaces

Learn more about JSON formatting

What is this tool?

JSON (JavaScript Object Notation) is a lightweight text format used to exchange structured data. It is the default format of most web APIs, and is widely used for configuration files, logs and NoSQL databases.

This tool turns compact or poorly indented JSON into a readable document (Format), or does the opposite by removing all unnecessary whitespace (Minify). It also validates the syntax: if the input is not valid JSON, the parser error is displayed.

Typical use cases

Inspecting an API response copied from the browser developer tools or a terminal.
Reviewing or fixing a configuration file (for example package.json or tsconfig.json ).
Reducing the size of a payload before embedding it in a request, a URL or an environment variable.
Sharing a readable snippet in a ticket, a code review or documentation.

How to use it

Paste your JSON into the text area.
Choose the indentation: 2 or 4 spaces.
Click Format to indent the document, or Minify to compact it on a single line.
Click Copy to copy the result to the clipboard.

Processing relies on the browser's native JSON.parse and JSON.stringify functions. Nothing is sent to a server, so the tool can be used with confidential data.

Before / after examples

Formatting (2 spaces)

Before

{"name":"DTK","tools":[{"id":1,"label":"JSON Formatter"}],"active":true}

After

{
  "name": "DTK",
  "tools": [
    {
      "id": 1,
      "label": "JSON Formatter"
    }
  ],
  "active": true
}

Minifying

Before

{
    "user": {
        "id": 42,
        "roles": ["admin", "editor"]
    }
}

After

{"user":{"id":42,"roles":["admin","editor"]}}

Formatting and minifying only add or remove whitespace between tokens. Spaces inside strings are always preserved, and the data itself is not modified.

Common syntax errors

JSON is stricter than JavaScript object syntax. The following mistakes are the most frequent causes of a parsing error.

Trailing comma after the last element

Invalid

{"a": 1, "b": 2,}

Valid

{"a": 1, "b": 2}

Single quotes or unquoted keys

Invalid

{name: 'DTK'}

Valid

{"name": "DTK"}

Comments

Invalid

{
  // Enables debug mode
  "debug": true
}

Valid

{
  "debug": true
}

Values that do not exist in JSON

Invalid

{"value": undefined, "ratio": NaN}

Valid

{"value": null, "ratio": null}

The error message comes from the browser's parser and usually indicates a position (a character index). The actual mistake is generally located just before that position.

Good to know

The order of keys is preserved.
If a key appears twice in the same object, only the last value is kept.
Numbers are normalized: 1.0 becomes 1 and 1e3 becomes 1000 .
Integers greater than 9007199254740991 (2^53 − 1) lose precision, because JavaScript stores numbers as 64-bit floating-point values. Large identifiers should be transmitted as strings.
Unicode escape sequences such as \u00e9 are decoded and displayed as the corresponding character ( é ).

Precision loss example

{"id": 12345678901234567890}
→ {"id": 12345678901234567000}

Did you know?

JSON was popularized by Douglas Crockford in the early 2000s. He describes it as a format he "discovered" rather than invented, since it was already part of JavaScript.
JSON is defined by two equivalent standards: ECMA-404 and RFC 8259. The latter requires UTF-8 encoding for JSON exchanged between systems.
Comments were deliberately left out of the format, to prevent them from being used to carry parsing directives and break interoperability.
The original license of Crockford's reference implementation contained an unusual clause: "The Software shall be used for Good, not Evil."
Until ES2019, JSON was not strictly a subset of JavaScript: the characters U+2028 and U+2029 were allowed in JSON strings but not in JavaScript string literals.

Frequently asked questions

Is my data sent to a server?: No. All processing is performed locally by your browser. The content is neither stored nor transmitted.
Should I use 2 or 4 spaces?: It is a matter of convention. 2 spaces is the most common choice in the JavaScript ecosystem (npm, Prettier), while 4 spaces is the default of tools such as Python's json.tool . The best choice is the one already used by your project.
Are JSON5 or JSON with comments (JSONC) supported?: No. The tool follows the strict JSON standard (RFC 8259). Comments, trailing commas and single quotes must be removed before formatting.
Is there a size limit?: There is no fixed limit. Documents of several megabytes are handled without difficulty; beyond that, performance depends on the memory available in your browser.