For some time I have been looking for a video on Youtube or just tutorials on how to program in Java that the plugin checks the version of the plugin on spigotmc and if it is outdated, an in-game owner is informed.
There's a REST API for the resources on spigotmc: https://spiget.org/documentation/
You can get the version list via "Resource Details" and via "Resource Version" you can get details about a version.
There are also a couple of code examples: https://github.com/...e-Examples
Somebody wrote a little tutorial on spigotmc.org:
https://www.spigotmc.org/...r-updates/
You then of course have to execute the code that it executes in the onEnable method somewhere else (e.g. In the PlayerJoinEvent). You also have to replace the logger with the player you want to send the message to.
Thanks
