The Colour Contrast Analyser (CCA), maintained by TPGi, lets a user pick a foreground and background color directly from anywhere on screen, including images and design mockups, and instantly reports the resulting contrast ratio along with pass or fail results against WCAG’s AA and AAA thresholds for both normal and large text.
It is a standard tool in both design review and development QA, since it works on static mockups before a single line of code is written, catching contrast problems at the design stage rather than after a page has already been built.