@Nine @noiob from my experience: it's often better than nothing, but most of the time it does not contain all relevant information

Some random example: the alt text was as follows: a baby penguin is standing in the snow with the word yes written below it

(I rewrote the real alt text on this toot to add missing information)

@Nine @noiob (I think it improved much during the last few years? Maybe they switched to using image detection and not user generated tags?
I remember those having descriptions/alt text like "mind blown gif"

@Nine @noiob
Okay, this one is terrible:
a man with glasses is surrounded by a glowing circle and the website pmitf.com is displayed below him

@Larymir @Nine from this very representative sample courtesy of the only four gifs I ever used this feature for, yeah it's probably image detection done on a static frame bc video to text is new and expensive

@noiob @Nine ah, the theory that only a single frame is used for the generation of the alt text seems like a likely explanation and is also helpful for ones own usage: if the important thing about the gif is some text that is visible in all frames, the alt text is probably okayish if you just want to convey the basic meaning (without any details)
Otherwise it is most likely useless or even misleading