Ask HN: Which tools have made you a much better programmer?

Getting better at coding is usually a long, slow process of study and practice. However, sometimes I run into something that's easy to understand and, once I'm using it, feels like I've leveled up.

A few personal examples are: * version control - specifically, reading up on git and understanding the more complex commands * debuggers * flame graphs for performance debugging * good code search

What have you added to your workflow that's made you much more productive?