What it does
Rewrites a JSON document in its smallest valid form: every space, newline, and indentation character between tokens is removed. The input is parsed first, so the output is guaranteed to be valid JSON carrying identical data. Invalid input produces a red error box, never broken output. A savings badge in the output header reports the before and after size in bytes and the percentage saved, computed to one decimal — green when bytes were removed, neutral when the input was already compact. Everything runs locally in your browser.
How to use it
- Paste JSON into JSON input (left), or tap a chip under Try: — Pretty config, Whitespace-heavy, or Already minified — to see each case minify. Sample loads a demo document; Clear empties the box.
- The minified document appears live in Minified (right), with the savings badge above it:
N bytes → M bytes · saved X%. - Copy takes the output; Download saves it as
minified.json(offered only when the input is valid JSON). - Copy share link encodes your input in the URL. Opening that link puts the input straight back into the tool.
Examples
Tap Sample:
78 bytes → 64 bytes · saved 17.9% — {"name":"CosmoDev","tools":["json-minify","base64"],"open":true}
The Whitespace-heavy chip shows both rules at once — padding between tokens vanishes, spaces inside a string survive:
{ "greeting" : "hello world" } → {"greeting":"hello world"} (67 bytes → 41 bytes · saved 38.8% for the full chip document)
An already-minified document stays as it is:
{"a":1,"b":[1,2]} (17 bytes) → {"a":1,"b":[1,2]} (17 bytes) · saved 0%
Minification can make a document longer, because JSON number formatting is normalized on re-serialization:
{"a":1E3} (9 bytes) → {"a":1000} (10 bytes) · saved -11.1%
The negative number is not a bug; it is the honest size difference.
How JSON minification works
Minification removes whitespace only. It shortens no keys, drops no data, and reorders nothing: parse the input, then serialize it back with zero separator characters. The operation is exactly reversible — formatting the minified document restores a readable form with the same content.
Because commas, colons, and brackets already delimit tokens, every whitespace character between them is optional:
| Pretty | Minified | Removed |
|---|---|---|
{\n "a": 1\n} |
{"a":1} |
newline, indent, space after : |
The one exception is whitespace inside a quoted string: it is data, and it survives untouched. A sentence inside a value keeps its spaces after minification.
Minified payloads matter wherever bytes are counted repeatedly: config files fetched by browsers, API responses served at scale, JSON embedded in a URL or a single-line script tag, and command-line one-liners where newlines break shell quoting.
Good to know
- Private: parsing and serialization run locally; nothing is sent anywhere.
- Equivalent to
JSON.stringify(JSON.parse(input)). - Watch the sign: 0 or negative savings means the input was already compact. The output is still the canonical form.
- Share links carry the full input in the URL — very large documents make very long links.
- Related tools: JSON Formatter, JSON Validator, JSON ↔ CSV Converter.