Check any text-on-background pair against WCAG 2.1 AA & AAA. Pick your colours, see the exact ratio, what passes, and a real preview. Everything runs in your browser — nothing is stored or sent.
21 : 1
AA
Normal text
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AA
Large text
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AAA
Normal text
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AAA
Large text
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Large text — headings & 18pt+
Normal body text. The quick brown fox jumps over the lazy dog — does this read comfortably at this size?
“Large” = 18pt (24px) or 14pt bold (≈18.7px) and above. AA needs 4.5:1 normal / 3:1 large; AAA needs 7:1 / 4.5:1. Non-text UI (icons, borders, focus rings) needs 3:1 (WCAG 1.4.11).
Why it matters: contrast is the single most common accessibility failure in teaching materials — slides, PDFs, LMS pages. Designing to AA from the start saves a remediation scramble later, and helps every learner in a bright room or on a cheap projector. This is a self-check, not a substitute for a full WCAG audit.
A free tool from NTLSN.com · WCAG 2.1 relative-luminance method · no data leaves your browser.