Ok, I spent about 30 min to an hour trying to figure out a problem with a test plugin. This is the second time this has happened to me, and is very frustrating. Declare your namespace. If you see something like that above, you have done 1 of 3 things: Forgotten to declare namespace. DevTools will not be able to find your main class if you don't, and this is very frustrating. A namespace, for the new people, is basically a way of organizing code, usually in separate folders. Example: Code: namespace author\exampleplugin; You forgot to type the path of your main class in plugin.yml . If you're following the setup like here, be sure to omit the 'src' part of your path, and also omit the '.php' at the end of it. Example, instead of this: Code: #plugin.yml main: src\author\exampleplugin\MainClass.php Use this: Code: #plugin.yml main: author\exampleplugin\MainClass You typed the wrong path. Look carefully at what you typed, and fix it. I know this was a short thread, but I don't want anyone else (especially new people) to have to stress out for an hour figuring this out.