Add vendor prefixes to CSS properties for cross-browser compatibility with configurable browser targets.
Paste CSS, pick a browser target, and get back the same stylesheet with only the vendor prefixes your target requires. Every property and selector is checked against browser-support data - the same Can I Use database the build-time Autoprefixer uses - restricted to the browsers you chose, and the needed -webkit-, -moz- or -ms- forms are inserted. Two things surprise people: with modern targets like 'last 2 versions' the output is often identical to the input, because current browsers need almost no prefixes, and the tool also removes prefixes no targeted browser requires, so hand-prefixed CSS can come back smaller. Everything runs in the browser; your CSS is never uploaded.
A concrete input and expected output from the current implementation.
Input
a {
position: sticky;
user-select: none;
} Expected output
a {
position: -webkit-sticky;
position: sticky;
-webkit-user-select: none;
user-select: none;
} With the browser target set to Safari 12, which supports both properties only with the -webkit- prefix, the tool emits the prefixed declarations ahead of the standard ones, which stay last and win wherever unprefixed support exists. Repoint the target at current Safari and the same input returns unchanged.
You choose a browser set from presets like 'last 2 versions' or '> 1%', or type an explicit list such as 'Safari 12, Firefox 78'. Each property and selector is matched against the support table for exactly those browsers, and a prefix is emitted only when at least one targeted browser still requires it. Declarations the whole target supports unprefixed pass through untouched.
The tool does not just add prefixes. Hand-written prefix stacks in your input are rewritten against the target: prefixes no targeted browser needs are deleted, ones still required are kept, and the unprefixed declaration is always placed last so it wins in browsers that support it. This is why already-prefixed CSS often comes back visibly smaller, and why the tool belongs at the end of a build pipeline.
Because with a modern target set - 'last 2 versions', or percentage thresholds that exclude old browsers - nearly nothing needs a prefix anymore. Current Safari, Chrome and Firefox accept unprefixed flexbox, transforms, gradients and most other once-prefixed features. An identical result is the tool working correctly, not a failure. Switch the target to an older browser set and prefixes will appear.
Only if some of your visitors use a browser that still requires them. In practice that means older Safari and iOS Safari for a short list of properties such as user-select, backdrop-filter and mask-image. If your analytics show only recent browsers, skipping prefixing entirely is defensible. If you must support old locked-down devices, they must be in the target list or they receive nothing.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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