Most of what modern software engineers do1 involves APIs: public interfaces for communicating with a program, like this one from Twilio. I’ve spent a lot of time working with APIs, both building and using them. I’ve written public APIs for third-party developers, private APIs for internal use (or consumption by a single frontend page), REST and GraphQL APIs, and even non-network interfaces like the ones for command-line tools. Like designing good software systems, I think much of the advice floa...