<li> [[mw:Composer/For extensions]] on using Composer to manage extensions
<li> [[mw:Manual:composer.json best practices]] for how to add Composer support to your extensions (including extension.json and skin.json)
<li> Jeroen DeDauw wrote [https://www.entropywins.wtf/blog/2013/11/24/introduction-to-composer-for-mediawiki-developers/ this blog post in 2014] that is probably still not only relevant, but also contains wisdom not addressed in other places (e.g. Extension developers should specify <code>"type": "mediawiki-extension"</code> in their extension's composer.json so that Composer installs your package into the 'extensions' folder instead of the typical 'vendor' folder that is Composer's default.)
</ol>