Color Contrast Checker Guide
A contrast checker tests foreground and background color pairs against WCAG accessibility standards, reporting the contrast ratio and which compliance level the combination passes. Designers use it during mock reviews, developers when implementing color tokens, and accessibility auditors when certifying sites against WCAG 2.1 or 2.2. The tool catches low-contrast combinations that look fine on a calibrated monitor but fail for users with visual impairments. It is the difference between a design that merely looks good and one that everyone can actually read. The checker parses your foreground and background colors, converts each to relative luminance using the sRGB-to-linear formula specified by WCAG, then computes the contrast ratio as the lighter luminance plus 0.05 divided by the darker luminance plus 0.05. The ratio is compared against WCAG AA thresholds of 4.5:1 for normal text and 3:1 for large text, and AAA thresholds of 7:1 and 4.5:1 respectively. The tool flags failures clearly so you know exactly which combinations need rework. Optional simulation modes preview how the pair looks to users with common color vision deficiencies.