[johnfn]

A pretty easy way to construct a bug that is easy for a human to solve but difficult for an AI is to have it to do something with z-indexes. For instance, if your element isn't rendering because something else is on top of it, Claude will struggle, because it's not running a browser, so the only way it could possibly know there was a bug would be to read every single CSS and HTML file in your entire repo. On the other hand, a human can trivially observe the failure in a browser and then fix it.

This is a pretty simple thing, but you can imagine how CSS issues get progressively more difficult for AIs to solve. A CSS bug can be made to require reading arbitrarily much code if you solve by only reading code, but by looking at relatively few elements, if you look at the page with your eyes.

This can be somewhat solved by hooking up a harness to screenshot the page and feed it into the AI, but it isn't perfect even then.