WebAIM Contrast Checker
A free web tool from WebAIM that checks whether two colours meet WCAG contrast requirements for normal text, large text and interface components. The quickest way to stop choosing colours that nobody can read.
Tool
Web Development
WebAIM
All
Free
What it is
The WebAIM Contrast Checker is a free web page where you enter a foreground and a background colour and see their contrast ratio, with pass or fail results for WCAG levels AA and AAA. WebAIM is a non-profit accessibility organisation based at Utah State University, also known for the WAVE accessibility checker.
The rules it checks
The page summarises the WCAG requirements as of 2026-09:
- Level AA requires a contrast ratio of at least 4.5:1 for normal text and 3:1 for large text.
- WCAG 2.1 and later require at least 3:1 for graphics and user interface components, such as form input borders.
- Level AAA requires 7:1 for normal text and 4.5:1 for large text.
Why it matters
Low contrast is one of the most common accessibility failures on the web. It affects people with low vision and ageing eyes, and everyone reading a phone in bright sunlight. Checking colours with a tool rather than by eye avoids choices that look fine on a bright laptop and fail everywhere else.
How to use it
- Check every text colour against its background when you build a palette, not after the design is finished.
- Check placeholder text, helper text, disabled states and links, which are the usual failures.
- Check input borders, icons and focus indicators against the 3:1 rule for interface components.
- Check both light and dark themes.
- Use the lightness sliders to find the nearest colour that passes.
The page also offers an API that returns the ratio and pass or fail states as JSON, which developers can use in scripts.
Free or paid?
Free. WebAIM also sells accessibility audits and training to organisations; you do not need them to use the tool.
Limits
It checks one pair of colours at a time. For whole pages, use WAVE or a browser extension, and remember that contrast is only one part of accessibility.
What you can do after
Build colour palettes that pass WCAG AA from the start, and explain contrast decisions in critiques and handoffs.
Common questions
What counts as large text? WCAG defines it by size and weight; the page links to the definition.
Does passing AA mean the design is accessible? It means the colours pass one criterion. Focus, structure, labels and more still need checking.
Ready to start?
Opens on WebAIM in a new tab.
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