About this contrast checker
Pick a text color and a background color and the tool computes the WCAG contrast ratio using the relative luminance formula (sRGB channels linearized, then weighted 0.2126R + 0.7152G + 0.0722B). The ratio ranges from 1 to 21 — the higher, the stronger the contrast and readability.
Results are graded against four WCAG thresholds: normal text AA ≥ 4.5 and AAA ≥ 7; large text (≥18pt, or ≥14pt bold) AA ≥ 3 and AAA ≥ 4.5. A live preview renders real text in the chosen colors so you can judge readability at a glance. Everything is computed locally in your browser.