CSS Autoprefixer Online for Free
The CSS Autoprefixer reads your modern stylesheet and automatically writes a vendor-prefixed copy of every property that still needs one for older browsers.
A typical design system update slows down when you write modern declarations like flexbox or transform and realize older browsers still need the fallback lines. Typing the Safari or older Edge prefixes by hand across a massive file introduces typos and creates duplicate lines that are hard to maintain.
Pasting the file here inserts the correct fallback copy above the standard declaration instantly while a live stats bar counts the new lines.
How to Use the CSS Autoprefixer
- Bring the CSS in: paste it into the editor on the left, drag a .css file onto the input panel, or click Upload CSS in the toolbar.
- Read the color-coded legend: blue for -webkit-, purple for -moz-, green for -ms-, and orange for -o- so you can tell at a glance which browser family each new line is targeting.
- Watch the stats bar: input size, prefixed output size, and the count of lines the prefixer added show up live as you type or paste.
- Take the output out: Copy puts the prefixed CSS on your clipboard, Download saves it as a .css file named after the active tool.
Tools Bundled in AIFreeForever's CSS Autoprefixer
Vendor Prefix Pass
Fallback lines for transform, transition, flexbox, and other modern features are written above the standard declaration.
Gradient Detection
When a background uses linear-gradient, the older forms land above the modern one automatically.
CSS Beautify
CSS Validate
Walks the file once and names every unclosed brace, missing semicolon, and bad hex color by line number.
Variable Extractor
Every custom property gets pulled into one root block so you can audit design tokens in a single read.
CSS Minify
Strips comments and collapses whitespace to create the smallest possible valid code before deployment.
Why Choose AIFreeForever's CSS Autoprefixer
| Capability | AIFreeForever | Typical Online Tools |
|---|---|---|
| Prefix Families Covered | -webkit-, -moz-, -ms-, and -o- on a single pass | -webkit- only |
| Flexbox Mapping | justify-content and align-items map to the -ms-flex-pack and -ms-flex-align spellings for IE10 and IE11 | Skipped |
| Live Stats | Input size, output size, and prefix-lines-added shown as you type | No feedback until copy |
| Included Utilities | Minify, validate, and variable extract from the same sidebar | Single-purpose page |
| Processing Location | CSS stays in your browser, nothing posted to a server | Requires an active server upload |
Who Is the CSS Autoprefixer Made For
Build engineers use the CSS Autoprefixer to insert every required vendor prefix in one pass, avoiding the hours wasted writing browser fallbacks manually across a large interface file.
Cleanest way to add vendor prefixes to a modern stylesheet
Because each prefixed line drops in above the standard declaration, the modern property stays intact for browsers that support it.
Live Prefix Stats
A stats bar names the byte difference and the count of prefix lines added as you type, so you can see the cost.
Color-Coded Legend
Each prefix family has its own color so you can scan the output and tell which browser a new line is targeting.
Stays in Your Browser
Source CSS and the prefixed output both stay in the tab so a private design system never reaches a third-party log.
