Been seeing some alt text that I don't think are very helpful lately, so some tips since I think the point is to be more inclusive!
If you're sharing a screenshot of some text, please copy the text you screenshot into the alt text. It doesn't help if your alt text says "screenshot of Twitter", for example (or what I've seen in the past "screenshot of AO3"). Someone who cannot see your image will not be able to understand the context of your post.
If the text is too long, you can include it in a reply, or you can focus the alt text to the part in the image that you are referring to.