Enter two colours to get the WCAG contrast ratio and AA/AAA verdicts. If it fails, you get an alternative that keeps the hue and only changes lightness.
Notes
Uses the WCAG 2.x formula: (L1+0.05)/(L2+0.05), matching browsers and audit tools.
Large text means ≥18pt (~24px) or ≥14pt bold (~18.66px).
Semi-transparent colours use the given alpha as-is; blending with the background is not simulated.