Contrast Checker

WCAG 2.2 level AA asks for at least 4.5:1 for normal text and 3:1 for large text, which means 24px and up, or 19px and up when bold. AAA raises those to 7:1 and 4.5:1. Icons, input borders and focus rings need 3:1 against their surroundings.

From the relative luminance of the two colours, using the formula in the WCAG specification: the lighter luminance plus 0.05, divided by the darker plus 0.05. The result runs from 1:1, identical colours, to 21:1, black on white.

When a pair fails AA for normal text, the tool keeps each colour's hue and saturation and moves its lightness step by step until the pair reaches 4.5:1. You get the closest passing version of your text colour and of your background, and one click applies it.

It means the colour contrast is. Accessibility also depends on text size, spacing, focus states, motion and how the interface works with a keyboard and a screen reader. Contrast is the easiest part to get right and the most common one to miss.

Yes. The two colours are in the page address, so copying the link shares the exact pair.