p0deje/steep

Steep is a tool that adds static type checking to Ruby, helping you catch bugs before your code ever runs. Ruby is dynamically typed by nature, which means it won't stop you from passing a string where an integer is expected until the code actually executes and crashes. Steep fills that gap by letting you declare what types your variables and methods should accept, then checking your code against those declarations. The workflow has three main steps. First, you run a command to generate a configuration file that tells Steep which parts of your codebase to check. Second, you write type declarations in separate signature files, describing things like "the name method returns a String" or "contacts is an array of Email or Phone objects." Third, you run a check command, and Steep reports any mismatches, like a method that's declared but never implemented. It supports generics, union types, and nullable types. There's also a prototyping command that can scan your existing Ruby files and generate a rough draft of type signatures to get you started. This is useful for teams working on larger Ruby codebases where type-related bugs are costly and hard to trace. If you're building an app with hundreds of classes and want confidence that refactoring won't silently break something, Steep gives you a safety net. It's designed for gradual adoption, so you don't have to type your entire codebase at once. One notable aspect is that Steep does not infer types automatically from your Ruby code. You have to write the declarations yourself, which is more upfront work but gives you precise control over what gets checked. It also integrates with editors like VSCode and SublimeText, showing type errors inline as you write rather than only when you run a command at the terminal.