Tools
Measure it yourself
Two pieces of loupe that work without Claude. Both run in your browser and send nothing anywhere.
Contrast checker
Type any colour your browser understands, including oklch() and colours with transparency. The foreground is drawn over the background before measuring, as on a page. The ratio is cut, not rounded, to two places, so 4.499 shows as 4.49 and fails.
Enter two colours the browser understands: hex, rgb(), hsl(), oklch(), a named colour.
Measure any page
Add it as a bookmark, open any page, and click the bookmark. It runs scripts/measure.js, the script loupe runs during a review, on the page as you see it now, and opens a panel with the results: text that fails contrast, targets under 24 pixels, type sizes, motion that ignores reduced motion, and template defaults. Press Escape to close it.
Drag the first button to your bookmarks bar, or copy it and paste it as a bookmark’s address, which also works on a phone. Clicking it here measures this page. 37 KB, built from the skill’s own script.
It measures one width, one colour scheme and one motion setting: whatever your browser has now. A review measures twelve combinations. Some sites block bookmarklets with a Content Security Policy. If nothing happens when you click it, that is the likely reason; the browser console shows the block.