One of the most interesting things I ever saw about API design was a presentation by Casey Muratori called "Designing and Evaluating Reusable Components".

It's the first time I saw anyone acknowledge this profound insight: sometimes, writing a practically useful API entirely at the same level of abstraction simply isn't possible.

Looks like it's available here, now:

http://mollyrocket.com/9438

Also noteworthy is the "How to Design a Good API & Why it Matters" talk

video: http://www.youtube.com/watch?v=aAb7hSCtvGw

pdf: http://lcsd05.cs.tamu.edu/slides/keynote.pdf

One library I've found very useful to study is libcurl -- it has a very elegant degradation system. Easy things start out easy, and when the user chooses to handle more complexity she can switch to a lower-level set of calls.

Thanks for this post! This is the kind of content I wish HN had more of.

I appreciate the small reference to "The Elements of Style" by Strunk. That book has helped me refine not only my writing but also my software design.

This is an excellent little PDF that was very useful to me when I put together a recent talk titled "API Design Matters". It's amazing how a bit of energy spent focusing on an API's design can improve so many aspects of both using and developing said API.

API design is something I have been meaning to look into - thanks for the link.

If you're looking to save this link, it's on Proggit.

PDF version: http://www4.in.tum.de/~blanchet/api-design.pdf