CSS supports 3-digit shorthand HEX codes when each channel pair consists of identical digits. #FF0000 shortens to #F00, #336699 shortens to #369, and #FFFFFF shortens to #FFF. The browser expands each digit by doubling it: #F00 becomes #FF0000.
Shorthand only works when both digits in each pair match. #6366F1 cannot be shortened because 63 ≠ 66 ≠ F1. Our converter outputs the full 6-digit HEX code and indicates when a shorthand version is available.
In production CSS, use shorthand when possible to reduce file size. For CSS minification tools, this optimization happens automatically — the minifier replaces 6-digit HEX with 3-digit shorthand wherever valid.