Finding math articles of small length in a given journal
If you have access to Web of Science (and perhaps other databases), this is (kind of) straightforward.
Search for Journal of Algebra in Publication Name, limiting the date range at least initially to something reasonable. As of mid-September 2020, searching on year-to-date yielded 410 entries.
The search results can then be dumped into Excel, choosing to get the full record.
That record includes the start and end page number of each article. Add a column that is the difference of those numbers, and sort the sheet on that column. You may then need to go through and throw away things like editorials and whatnot.
Done.