Yes, you can post extensions here that don't use the API. There are several scripts/extensions/apps posted here that use undocumented interfaces(example) or even screen scraping(example).
The extension must make use of the API and/or enhance one or more Stack Exchange sites.
- Etiquette of Screen-scraping Stack Overflow?
- Stack Exchange Network Terms of Service
- Guidelines for the Use of the Stack Exchange Trademarks
You should use the API for your data as much as possible.
This theoretically avoids undocumented changes and staves off the ban-hammer.
In this case, you are fetching unread counts of notifications and inbox items.
There are existing API routes for both:
Ideally you would use these and not that URL. Although it can be quite a bother in this case, since both routes require OAuth and an
However, the URL might also yield unexpected results if the extension user is not authenticated and depending on how the extension calls it (It mostly reads as all zeroes, falsely, when not called as expected by the server).