Today's developer tools are mostly used in a very technocratic fashion where there's success and failure, 1 and 0. Either a tool thinks you're totally wrong or you're 100% right. You get shouted at or praised. There is no middle ground. Except there is. Credo, the first teaching code linter for Elixir, puts its focus on the in-between: How errors can be opportunities for learning. How AST analysis can be fun and educational. And how one can combine these features into a professional tool that gives straight results while still treating its users as human beings.