The Web Content Accessibility Guidelines (WCAG) provide a set of recommendations describing how to produce websites that are more accessible for people with disabilities and that work well across a range of devices. These guidelines specify the minimum levels of contrast between text and background colors necessary for pages to be easily readable. The WebAIM Color Contrast Checker provides an interactive tool to check a given pair of colors. The tool also allows users to interactively adjust the lightness of their provided colors, updating the computed contrast ratio automatically as changes are made. The resources block on the top right of the page provides links to detailed technical descriptions of how colors are checked. For more technical users, the Color Contrast Checker can also be used as a REST API. An example of API usage is provided at the bottom of the page. The WebAIM Color Contrast Checker works in any modern browser.