WCAG 3.0 APCA Checker

WCAG 3.0 APCA Checker previews the direction of the next accessibility contrast model, applying a single perceptual-style gate to a text and background pair.

What is WCAG 3.0 APCA Checker?

WCAG 3.0 APCA Checker previews the direction of the next accessibility contrast model. It pairs a foreground and a background, prints the contrast figure to two decimal places, and judges it against a single threshold, with the panel labelled as an approximation of APCA rather than as an implementation of it.

The APCA work exists because the WCAG 2.x ratio has a well-known weakness, and knowing what it replaces is the point of this page:

• The older ratio is symmetric, so dark text on a light background and light text on a dark background score the same even though they do not read the same.
• The older ratio is not perceptually uniform, so equal steps of ratio do not correspond to equal steps of perceived contrast.
• The older ratio ignores polarity, text size and font weight entirely, which is why a 4.5 to 1 result can describe two pairs that feel completely different.
• APCA reworks the model around polarity and lightness, and reports a lightness contrast value rather than a ratio.

The figure this page prints comes from the WCAG 2.x contrast ratio calculation, rounded to two decimals, compared against a 4.5 to 1 gate. No APCA lightness contrast value is computed, and the panel heading says as much. That makes the page useful as an orientation aid, letting you see how an existing pair sits against a familiar number while you read up on the newer model, but not as evidence about how APCA would score the same pair.

Reading the printed figure as an APCA contrast score is the trap to avoid. What is on screen is a perceptual contrast figure in the WCAG 2.x tradition, and the polarity contrast question that motivates the newer model is left entirely unanswered by it. The quickest way to see the difference the model is arguing about is to compare a dark-on-light pair with the same two colors inverted, and note that this page returns identical numbers for both.

Because the panel is an approximation, its limits are the important part.

• The number is the WCAG 2.x ratio. It cannot be quoted as an APCA lightness contrast value, and the two are not interchangeable.
• Polarity is not modelled. Swapping the two colors returns the same figure here, whereas an APCA score would not.
• Text size and font weight do not change the result, though both are inputs to the newer model.
• The 4.5 to 1 threshold is borrowed from WCAG 2.x AA. It is not an APCA threshold, because APCA does not define one.
• Two colors only, with no alpha and no surface behind them.

Treat this page as a preview and a signpost. For a compliance decision today, the AA and AAA checks are the ones that map onto a published standard, and this page is the right place to start when you suspect that a ratio-shaped threshold is the wrong tool for a pair that simply does not read well.

How to use WCAG 3.0 APCA Checker

1. Enter the foreground color and the background color in the two swatch fields.
2. Read the panel heading, which labels the figure as an APCA approximation and gives it to two decimal places.
3. Compare the Pass or Fail line against the 4.5 to 1 gate shown beside it.
4. Swap the two colors and re-read the unchanged figure, which is the quickest way to see the polarity limitation for yourself.

When to use WCAG 3.0 APCA Checker vs related tools

Use the WCAG 3.0 APCA checker when you want to know how a pair will look against a familiar ratio gate while you evaluate the perceptual model that is likely to replace it. For published compliance, the WCAG 2.1 AA checker and WCAG 2.1 AAA checker are the checks that map onto WCAG 2.1 itself, the contrast checker shows all four WCAG 2.x thresholds at once, and the text readability checker is the place to go when a pair passes on paper but still reads poorly in practice.

Privacy & Security

This tool runs entirely in your browser — no data ever leaves your device. There is no server round-trip, no upload, no logging, and no account required. Your input is processed locally using client-side JavaScript and is never stored, transmitted, or accessible to anyone else. When you close the tab, everything disappears.

Frequently asked questions about WCAG 3.0 APCA Checker