Drop in any two colours — hex, rgb(), hsl(), or named — get the WCAG 2.1 contrast ratio plus a per-criterion breakdown across AA (normal + large) and AAA (normal + large). With a live preview swatch so you can see what the combination actually looks like.
Large text per WCAG = ≥ 18pt regular or ≥ 14pt bold. Anything smaller falls under the normal-text rule.