ACT Rule 09o5cg
Text has enhanced contrast
This is the Level AAA version of the contrast check. It measures the highest contrast each character can reach against its background and compares that with the 7:1 the enhanced criterion asks for, or 4.5:1 for large text.
A tool can decide this one on its own, which is why it turns up in scanner output. The rule is approved, which in W3C's process means it was implemented in full by at least one tool or methodology and then signed off by a working group. Approval is a statement about tools, not a statement that this is the settled way to test the criterion.
What passing this rule proves
When this rule fails, 1.4.6 Contrast (Enhanced) is not satisfied, and that half is certain. When it passes, W3C's own outcome mapping says the criterion still needs further testing. So a green result here is evidence that one specific thing is not broken, and it is the answer W3C gives on 59 of its 87 live rules.
W3C is blunt about the limit of this measurement on the rule page. When some pixels behind the text clear the ratio and others do not, there is no agreed way to decide whether the text is legible, so passing does not mean the contrast is sufficient. Text over a photograph is the everyday case. Results also vary from one browser to another.
The criteria this rule is a test for
These are the criteria the rule names as its own conformance requirement. Each one is a far bigger question than this rule asks, and our page for it sets out what the whole criterion covers.
- 1.4.6 Contrast (Enhanced) Level AAA
Criteria that are related but not tested here
W3C calls these secondary requirements. The rule correlates with them and was not designed to test them, so each one is either stricter than the rule or can be satisfied in ways the rule never looks at.
- 1.4.3 Contrast (Minimum) Level AA
The normative rule text lives at W3C
What the rule applies to, and exactly what it expects, is published by W3C and can change. We link to it rather than restate it, so nothing here can quietly fall out of date against the source. Read rule 09o5cg at W3C.
Contrast between text and background is measured as a ratio
Text has to stand far enough apart from what sits behind it, measured as a ratio between the two. Normal text needs 4.5 to 1 at AA. Large text needs 3 to 1, and AAA raises both.
This is not about people who are blind. It is about the far larger number with low vision, ageing eyes, or a screen in daylight.
Grey placeholder text and light text over a photograph are the two that turn up in nearly every audit. Both usually look fine on the designer's monitor but fail the ratio on other screens.
Fixes that satisfy it
If this rule fails on your site, these are the techniques that put it right.
Other rules W3C files under the same criteria
Each of these asks a different question about the same part of the standard. Passing all of them is still not the same as satisfying the criterion.
- Text has minimum contrast A tool can check this
All 87 ACT rules are grouped by the criteria they test, and 24 of them decide nothing about WCAG on their own. Run a free scan to see which of these your own pages trip.