Accessibility prompts: measure contrast and describe image purpose

Last updated: 7 Oct 202611 min read

tutorial

A contrast prompt needs the actual foreground and background colors for each rendered state, including hover, disabled, and error states where they matter. A screenshot estimate is not a color measurement; overlays and gradients can change the effective pair. Text alternatives require the image's function in context. A linked logo may need the destination name, while a decorative mark should not repeat nearby text. Ask the model to list measurements and purpose judgments separately so neither masquerades as a complete accessibility audit.

Operational case

Harbor's pickup warning uses muted orange text on a light card. The reviewer samples the computed foreground and the effective card background, checks the measured ratio against the team's applicable criterion, and records the values. The delivery-map icon beside 'Pickup zone' adds no information and should not force a repeated announcement. A different map image showing the actual pickup zone needs an alternative that communicates the location or an equivalent text description.

Warning state: inspect computed foreground/background pair
Measure: actual rendered colors, not screenshot estimate
Decorative icon: avoid repeated name
Informational map: provide location meaning in text
Verdict: only after criterion and context are checked

Performance and review cost

Measuring C color pairs is O(C) checks; inspecting I images for purpose is O(I) human judgments. Gradient and overlay states may require several samples per component. A prompt can prepare the inventory, but a single measured pair and one alt-text pattern cannot cover every state or image role.

Common Mistakes

Do not estimate a pass from a screenshot.
Do not give every image the same generic alternative.
Do not ignore state-dependent colors.

Connected lessons

prompt engineering

accessibility review