This tool measures the contrast ratio between two colors and checks them against the Web Content Accessibility Guidelines (WCAG 2.1). It's how you make sure text is readable for everyone, including people with low vision.
WCAG sets thresholds: AA needs a ratio of at least 4.5:1 for normal text and 3:1 for large text; AAA is stricter at 7:1 and 4.5:1. The badges update live as you change either color.
Each color is converted to relative luminance using the sRGB formula, then ratio = (L1 + 0.05) / (L2 + 0.05), where L1 is the lighter color. Results range from 1:1 to 21:1.
WCAG defines large text as roughly 18pt (24px) regular or 14pt (18.66px) bold and above.
Use hex colors for accurate results; alpha values are not measured here, so flatten your colors first.