Plugins can load and use any DLL's including referencing all .NET frameworks DLL's and do P/Invoke, just like a regular .NET program.
If you get a "System.NotSupportedEception: An attempt was made to load an essembly from a network location" error while trying to load a plugin, try unblock the dll file as shown here
Plugin API v2¶
Documentation for the API can be found at https://adiirc.github.io/apiv2/generated/.
Visual studio template for creating a plugin can be found at https://github.com/AdiIRC/apiv2/tree/template.
Great tutorial by MoonWolf for how to do various things with the API https://github.com/AdiIRC/apiv2/tree/master/docs/tutorial.
Plugin source can be found at https://github.com/AdiIRC/apiv2.
Plugin API v1 (deprecated)¶
Documentation for the API can be found at https://www.adiirc.com/docs/.
You can download a sample plugin in Visual Studio C# Express format at https://www.adiirc.com/plugins/MyPlugin.zip
You can download Visual Studio Express at https://www.microsoft.com/express/download/