The current format of MediaWiki thumbnail URLs is very ad hoc: it depends on the media handler, the contents of the file, and a dozen different configuration settings. As a consequence, it is impossible to guess what a thumbnail URL will be, given the filename and the desired size; clients have to request it from the AP and waste hundreds of valuable milliseconds, or use complicated logic to guess it and accept that sometimes they will end up with the wrong result.

There is an ongoing discussion about rethinking the URL format so that it can be used as a proper API. [1] As part of that, I would like to make a list of clients which try to guess thumbnail URLs on their own, instead of fetching them from the API - these clients will need to be updated if we change the URL format. If you know of any, please add them to T153498 [2], and preferably some information on what they do. Clients can include mobile apps, user scripts, bots, whatever you can think of.

Thanks!

[2]: https://phabricator.wikimedia.org/T153498