Implementing features such as auto-complete or go-to-definition for a programming language is not trivial. Traditionally, this work had to be repeated for each development tool and it required a mix of expertise in both the targeted programming language and the programming language internally used by the development tool of choice.
The Elixir Language Server (ElixirLS) provides a server that runs in the background, providing IDEs, editors, and other tools with information about Elixir Mix projects. It adheres to the LSP, a standard for frontend-independent IDE support. Debugger integration is accomplished through the similar VS Code Debug Protocol.
These pages contain all the information needed to configure your favourite text editor or IDE and to work with the ElixirLS. You will also find instructions on how to configure the server to recognize the structure of your projects and to troubleshoot your installation when things do not work as expected.