Unfortunately the xkcd "alt text" is, rather than an alt text, an additional component of the joke which doesn't make sense without the picture. You Had One Job, Dude.
@alcinnz next up: browser plugin to replace xkcd links with explainxkcd links, to go along with replacing twitter links with nitter links, etc...
(I did have to search for this since I somehow remembered this version existed, but it doesn't seem to be linked from anywhere on the current main xkcd site...)
Also each comic has an accompanying info.0.json file in the same directory that contains the alt text (and a comic transcript, when available) - admittedly not immediately useful.
@feonixrift The weird thing is that if you look at the source, some of them do have transcripts, but it's hidden with CSS, which makes it inaccessible to screen readers (maybe it was originally made for text-based browsers, which wouldn't surprise me since hypothetical text-based browser users often seem to get more attention than all of the very real screen reader users out there).
@montag I used to use text based browsers enough to access xkcd thereby on occasion... alas, no, even then that text served only to assist the search engines in finding the correct comic when one half remembered its text and went googling.
@feonixrift XKCD puts the additional component in the "title" attribute of the image (not the "alt" one), so this is actually fine. This is common practice among many webcomics (an inherently visual art form) by the way and not specific to XKCD at all.
Unfortunately, the "alt" attribute only contains the name of the comic strip instead of an image description though, and I agree that it could be used in a much better way.
A bunch of technomancers in the fediverse. This arcology is for all who wash up upon it's digital shore.