Accessibility: Impose a limit on the length of alt text

[ZoeBijl]

Pitch

Set and communicate a character limit for alt text. The current limit of 1500 characters is too long. Twitter has a more sensible limit of 420 characters.

Motivation

420 characters is a lot of text. Screen readers will read the entire alt text in one go. Meaning users can’t navigate it word by word. If you need more than 420 characters you should consider a transcript.

This entire comment is exactly 420 characters.

[elaine-jackson]

It's not like all users are using the full 1500 characters for their alt text. I don't think we should lower the limit as it might be needed for a select few graphics. Also if we impose a software limit on the number of characters and prevent any more from being shared, what happens to older images using more than 420 characters for alt? Are they removed from federation for breaking protocol? Will the remaining characters simply not show up. If so this is a breaking changes that breaks old content.

[ZoeBijl]

The point is that any alt text longer than say 420 characters is unusable by most people that need it.

[Gargron]

The current limit of 1500 characters is too long

#11658

[elaine-jackson]

@ZoeBijl Instance owners can adjust the limits, Mastodon Project adjusting an arbitrary limit would have little effect unless all instance owners accept the change.

[mgifford]

I don' t think there are too many users entering 1500 character alt text. Still, I think that 420 characters is totally reasonable as upper limit. If it is much longer than that then probably other strategies would be better.

The W3C has some info on this https://www.w3.org/WAI/tutorials/images/complex/