https://bugzilla.wikimedia.org/show_bug.cgi?id=14869#c19

Slightly out of date, but serves as a starting point

Maintenance reports

• Broken redirects -
• Cross-namespace links (Extension) -
• Dead-end pages -
• Double redirects -
• Long pages -
• Oldest articles -
• Orphaned pages -
• Pages with the fewest revisions -
• Pages without language links -

list=allpage&sapfilterlanglinks=withoutlanglinks

• Protected pages -

list=allpages&apprtype=edit|move&apprlevel=sysop|autoconfirmed

• Protected titles -
• Short pages -
• Uncategorized categories -
• Uncategorized files -
• Uncategorized pages -
• Uncategorized templates -
• Unused categories -
• Unused files -
• Unused templates -
• Unwatched pages -
• Wanted categories -
• Wanted pages -

List of pages

• All pages - list=allpages&apfrom
• All pages with prefix - list=allpages&apprefix
• Categories - list=allpages&apnamespace=14
• Category tree - n/a
• Disambiguation pages - list=embeddedin&eititle=Template:Disambiguation
• Redirects - list=allpages&apfilterredir=redirects

Login / sign up

• Log in / create account - n/a

Users and rights

• Block user - n/a
• Blocked IP addresses and usernames - list=blocks
• Deleted contributions -
• Global user list - n/a
• My preferences - n/a
• User contributions - list=usercontribs
• User group rights - n/a
• User rights management - n/a
• Users - list=allusers

Recent changes and logs

• Gallery of new files - list=logevents&letype=upload
• Logs - list=logevents
• My watchlist - list=watchlist
• New pages - list=recentchanges
• Recent changes - list=recentchanges
• Related changes -

Media reports and uploads

• File path - n/a
• Files - list=allpages&apnamespace=6
• MIME search -
• Search for duplicate files -
• Upload file - n/a

Wiki data and tools

• Expand templates - action=expandtemplates
• Gadgets - n/a
• Parser diff test - n/a
• Statistics - n/a
• System messages - n/a
• Version - n/a

Redirecting special pages

• External links - list=exturlusage
• Random article - list=random
• Random redirect - list=random&rnredirect
• Search - list=search

High use pages

• Most linked-to categories -
• Most linked-to images -
• Most linked-to pages -
• Most linked-to templates -
• Pages with the most categories -
• Pages with the most revisions -

Page tools

• Cite - n/a
• Export pages - n/a
• Import pages - n/a
• View deleted pages - n/a
• What links here - action=query&list=backlinks

Other special pages

• Book sources - n/a
• List of globally blocked IP addresses - list=globalblocks
• Local status of global blocks -
• Login unification status - n/a
• Wikimedia Board of Trustees election - n/a
• Wikimedia wikis - n/a

For example, a user searching the page for the equivalent of "Special:WhatLinksHere" can't easily discover that such functionality is tucked away in list=backlinks.

For this specific example, what is the expectation? Do have a line "This resembles Special:WhatLinksHere." on https://en.wikipedia.org/w/api.php?action=help&modules=query%2Bbacklinks right after "Find all pages that link to the given page."? If yes, where should this be added? Simply appending another sentence to the string of the ID apihelp-query+backlinks-description in the language file? Somewhere else?

Seeing the list in T37234#404819 (which should be moved to the task desc nowadays?) this does not look like a small task anymore.
Feel free to re-add good first task once the task description covers the approach (how this should be added), actually contains an example for "current outcome" and for "expected outcome", and the scope of the task has made been clarified ("there are likely others").

In T37234#2896324, @Aklapper wrote:

For this specific example, what is the expectation? Do have a line "This resembles Special:WhatLinksHere." on https://en.wikipedia.org/w/api.php?action=help&modules=query%2Bbacklinks right after "Find all pages that link to the given page."? If yes, where should this be added? Simply appending another sentence to the string of the ID apihelp-query+backlinks-description in the language file? Somewhere else?

That would work. The other option would be to add another message apihelp-query+backlinks-userinterface or something, and if that message exists, display it under the description on the help pages

As @Anomie has done most of the API help restructuring, etc, he may be the best versed to suggest how to proceed :)

In T37234#2896324, @Aklapper wrote:

If yes, where should this be added? Simply appending another sentence to the string of the ID apihelp-query+backlinks-description in the language file?

If yes, I think that would be appropriate.

Maintenance reports

• Broken redirects - probably not existing in the API itself; but https://www.mediawiki.org/wiki/Manual:Pywikibot/redirect.py is the closest
• Dead-end pages - (not existing?)
• Double redirects - probably not existing in the API itself; but https://www.mediawiki.org/wiki/Manual:Pywikibot/redirect.py is the closest
• Long pages - (not existing?)
• Orphaned pages - somehow via https://www.mediawiki.org/wiki/API:Backlinks ???

Login / sign up

• Log in / create account - https://www.mediawiki.org/wiki/API:Account_creation and https://www.mediawiki.org/wiki/API:Login#How_to_log_in ???

High use pages

• Most linked-to templates - https://www.mediawiki.org/wiki/API:Lists/All#Alltransclusions ???

Users and rights

• Deleted contributions - https://www.mediawiki.org/wiki/API:Lists/All#deletedrevs ???

In T37234#2901879, @Aklapper wrote:

Maintenance reports

• Broken redirects - probably not existing in the API itself; but https://www.mediawiki.org/wiki/Manual:Pywikibot/redirect.py is the closest
• Dead-end pages - (not existing?)
• Double redirects - probably not existing in the API itself; but https://www.mediawiki.org/wiki/Manual:Pywikibot/redirect.py is the closest
• Long pages - (not existing?)
• Orphaned pages - somehow via https://www.mediawiki.org/wiki/API:Backlinks ???

You can access the results of these special pages via list=querypage.

Login / sign up

• Log in / create account - https://www.mediawiki.org/wiki/API:Account_creation and https://www.mediawiki.org/wiki/API:Login#How_to_log_in ???

Yes. More specifically, action=clientlogin is the equivalent to Special:UserLogin and action=createaccount for Special:CreateAccount.

High use pages

• Most linked-to templates - https://www.mediawiki.org/wiki/API:Lists/All#Alltransclusions ???

No, that just lists all transclusions without ordering by most-linked-to. Again, list=querypage allows access to the special page's output.

Users and rights

• Deleted contributions - https://www.mediawiki.org/wiki/API:Lists/All#deletedrevs ???

list=deletedrevs is deprecated. list=alldeletedrevisions with the adruser parameter would probably be the way to do it.