AltDetector 2.04 adds two new features:

Discord Webhooks

You can have AltDetector's alt messages sent to your Discord server. To use this, enable it in the config file and restart your Minecraft server.

PlaceholderAPI integration

You can now use a Placeholder to get the alts of players on your server. This is enabled by default if you use PlaceholderAPI. The format is:
%altdetector_alts_<playername>%
<playername> is case-sensitive. You can configure the separator between each alt in the config file.

Thanks to Sterile-Gaming for taking the initiative for adding these features.