Are my colors sent anywhere?

No. The contrast ratio is computed in your browser with the WCAG luminance formula. The color values you enter never leave your device.

What contrast ratio do I need to pass WCAG?

WCAG 2.1 AA requires at least 4.5:1 for normal text and 3:1 for large text (about 18.66px bold or 24px regular). AAA raises this to 7:1 and 4.5:1 respectively. UI components and graphics need at least 3:1.

What counts as "large text"?

Large text is roughly 24px (18pt) for regular weight or 18.66px (14pt) for bold. Large text is allowed a lower contrast threshold because bigger glyphs remain legible at lower contrast.

WCAG Color Contrast Checker

Check text and background colors against WCAG AA and AAA contrast ratios.

WCAG color contrast checker

Enter a text color and a background color and get the exact contrast ratio, plus clear pass/fail badges for WCAG 2.1 AA and AAA at normal and large text sizes — and the 3:1 threshold for UI components and graphics.

A live preview shows your colors on real sample text. The ratio is calculated in your browser using the official relative-luminance formula, so nothing is uploaded.