JSON formatter

Indent, minify and validate your JSON. Your data stays on your device.

Format, minify, validate

Paste your JSON into the field, then:

Format adds indentation and line breaks to make the structure readable;
Minify removes all unnecessary whitespace to reduce the size;
in both cases, the JSON is validated: if there is a syntax error, its position is shown.

"Copy" takes the result, "Clear" empties the fields.

The rules of JSON

JSON is stricter than the JavaScript it comes from. Most errors come from these rules:

Rule	Correct	Incorrect
Keys in double quotes	`{"name": 1}`	`{name: 1}`
Strings in double quotes	`"text"`	`'text'`
No trailing comma	`[1, 2]`	`[1, 2,]`
No comments	-	`// note`
Allowed values	`true`, `false`, `null`	`undefined`, `NaN`

Reading an error message

The position shown is often just after the real error: if the tool reports a problem at the start of a line, look at the end of the previous line, where a comma is often missing. Other suspects: an unclosed quote, or a bracket and a brace swapped.

When to format, when to minify?

Format to read an API response, debug a configuration file, or review data before editing it.
Minify to shrink a file served on the web or stored in bulk. The saving comes from removed spaces and line breaks; the data stays identical.

Sensitive data

API responses and configuration files often contain tokens, keys or personal data. Here, processing is entirely local: nothing is sent or stored. That is a real difference from many online formatters that process content on their servers.

Frequently asked questions

Is my JSON data sent anywhere?

No. Processing is 100% local; no data leaves your browser.

Why is my JSON rejected when it works in JavaScript?

JSON forbids what JavaScript tolerates: unquoted keys, single quotes, trailing commas and comments. Fix these and it will be accepted.

Does formatting change my data?

No. Only spaces and line breaks change; values, key order and structure stay identical.

Is there a maximum size?

Toolo sets no limit. Files of several megabytes work on a recent computer.