Pick a text colour and a background. You get the contrast ratio, a pass or fail for each WCAG level, and - when it fails - the closest shade of your text colour that passes AA.

Normal text looks like this. Can you read it comfortably?

Large text looks like this

- contrast ratio
  • AA - normal text (needs 4.5:1)
  • AA - large text (needs 3:1)
  • AAA - normal text (needs 7:1)
  • AAA - large text (needs 4.5:1)
  • Buttons, icons and form borders (needs 3:1)

Good to know

"Large" text means at least 24px, or 18.66px when bold. AA is the level most accessibility laws and audits ask for; AAA is stricter.