The character limit for alt texts when inserting images via the TinyMCE editor's media and AI image generator plugins has been increased from 125 characters to 750 characters in MDL-78453. 

Currently, the img_alt_is_too_long check sets a limit of 125 characters for the alt text and has a default severity of BA_TEST_SEVERE. Users entering an alt text greater than this value will get an error.

According to the Web Accessibility Initiative (WAI):

The alt text should be the most concise description possible of the image’s purpose. If anything more than a short phrase or sentence is needed, it would be better to use one of the long description methods discussed in complex images.

A 125-character limit for alt texts can be commonly found over the web. However:

• There is no formally defined limit for alt-texts.
• This can be attributed to screen readers' limitations in the past, which prevented them from reading alt texts that were more than 125 characters.
  • This is no longer the case, as current versions of screen readers (Narrator, VoiceOver, JAWS) can read long alt texts in full, except for NVDA, which breaks down long alt texts in chunks of 100 characters.
• Accessibility checkers like axe DevTools, WAVE, Silktide, etc., also don't raise errors or warnings for long alt texts.

We should consider:

• Downgrading the severity of relatively long alt texts to BA_TEST_SUGGESTION.
• Updating the checkdesc:imgaltisdifferent lang string for the check from:

  Image alt (alternative) text should not be more than the maximum allowed (125) characters.

  to something more of a reminder/suggestion, like

  Ensure that the image alt (alternative) text is concise enough to describe the image.

• And perhaps increasing the character limit. Conciseness is subjective, so a limit of 125 characters may be a bit too strict.