Color constrast helpers to achieve the WCAG 2.0 standard

Usage no npm install needed!

<script type="module">
  import opendevtoolsWcagColor from 'https://cdn.skypack.dev/@opendevtools/wcag-color';


WCAG Color

npm (scoped)

According to the WHO an estimated 1.3 billion people live with some form of visual impairment. This includes people who are legally blind and people with less than 20/20 vision.

This library helps you achieve the accessibility standards for color contrast outlined in the WCAG 2.0 specification.


npm install @opendevtools/wcag-color



ratio takes two colors, a foreground color, and background color, and returns a contrast ratio. ratio accepts most color formats:

  • HEX - normal (#0088ff), shorthand (#08f) and without hash (08f)
  • RGB - rgb(255, 255, 255)
  • HSL - hsl(210, 100%, 40%)
ratio(foreground: string, background: string) => number


import { ratio } from "wcag-color";

ratio("hsl(210, 100%, 40%)", "#ffffff"); // 5.57


score takes two colors and returns a score value. Read more below.

score(foreground: string, background: string) => 'Fail' | 'AA Large' | 'AA' | 'AAA'


import { score } from "wcag-color";

score("hsl(210, 100%, 40%)", "#ffffff"); // AA

Score from ratio

scoreFromRatio takes a ratio and returns a score value.

scoreFromRatio(ratio: number) => 'Fail' | 'AA Large' | 'AA' | 'AAA'


import { scoreFromRatio } from "wcag-color";

scoreFromRatio(7.5); // AAA

Best color out of two

best takes two colors and a background color and returns the color which is best suited, from a contrast perspective, for that background color.

best(firstColor: string, secondColor: string, background: string) => string


import { best } from "wcag-color";

best("#ffffff", "#000000", "#ffffff"); // #000000

Score and ratio

  • Fail - Your text has a contrast ratio of less than 3.0
  • AA Large - Least amount of contrast for font size 18px and larger. The ratio is above 3.0.
  • AA - What you should aim for with text sizes below 18px. The ratio is at least 4.5.
  • AAA - Enhanced contrast with a ratio of at least 7.0. Valuable for texts that will be read for a longer period of time.