Color Contrast Checker
Runs entirely in your browser — nothing you type is sent anywhere.
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The ratio is compared unrounded
#070707 on #777777 is 4.4983…:1. A checker that rounds to two decimals shows 4.50:1 and calls it an AA pass — but WCAG's thresholds apply to the unrounded ratio, so it fails. That is why the same pair can pass in one tool and fail an audit. This checker compares unrounded, shows enough decimals to see why, and tells you explicitly when rounding would have flattered your pair.
Transparency is refused, not dropped
A semi-transparent color has no contrast ratio of its own — what you see depends on what is behind it. Most checkers silently drop the alpha channel and score a color you are not actually rendering. Here #77777780 is refused with the reason; composite over your real backdrop first, or check the opaque form. One honest limit, stated: the WCAG luminance formula raises channels to the power 2.4, which no exact arithmetic survives — the math is IEEE floating point, like every other checker; the difference is what we do at the threshold. As with every tool here, the page is static and keeps working offline, verified by our automated tests on every release.