Also I found Dialyzer (success typing checker) to be helpful in large projects:

http://learnyousomeerlang.com/dialyzer

The way success typing works it is a bit like static typing but when it cannot deduce the types it assumes success. However when it finds a discrepancy it is always right. So the more type annotations you add, and the more precise they are the more benefits you get from it.

It has also been there for many years. I think Python only very recently has started getting the same kind of things via MyPy. Of course, they had to call it something differently (Optional Static Typing).

Elixir has a wrapper around it, it seems: https://github.com/jeremyjh/dialyxir but never used it (I user Erlang mostly).

The wonderful thing about it is that you don't have to get all type annotations since the begining, you can add them over the time. This allows to use "unspecified" types for quick prototyping, and make them more specific when the project evolves, which is a major complain of traditional type systems such as Java's.

Another tool that I find useful is Credo[1] which "is a static code analysis tool for the Elixir language with a focus on teaching and code consistency".

The Ecto[2] project uses a tool called Ebert[3] that automatically runs Credo for each pull-request and comments with the issues found. Here you can see an example of Ebert's bot commenting on a PR[4]

[1] https://github.com/rrrene/credo [2] https://github.com/elixir-ecto/ecto [3] https://ebertapp.io/ [4] https://github.com/elixir-ecto/ecto/pull/1785