RequiredInterfaces.jl is a small package, allowing abstract-type based definition of interface methods, as well as some methods for checking whether a type that claims to implement an interface, actually implements the required methods.
Please check out the documentation to learn how you can use RequiredInterfaces.jl to provide basic "implement me" style interfaces in your library.
If you want to learn more about the motivation & philosophy behind this package, check out this writeup about APIs and their surface in Julia, which is part of the documentation of this package.