An accessibility checker tool for validating the color contrast based on WCAG 2.0 and WCAG 2.1 standard.
The formula (L1/L2) for contrast is based on [ISO-9241-3] and [ANSI-HFES-100-1988] standards as described here :
http://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef, external http://www.w3.org/TR/WCAG20/#contrast-ratiodef, external https://www.w3.org/TR/WCAG21/#contrast-minimum, external
It also supports shorthand color codes e.g #FFF or #000 etc.
https://www.w3.org/TR/2001/WD-css3-color-20010305#colorunits, external