Alex Bosworth over at Source Labs (and creator of the great open source resource SWiK) writes consistently good posts and Monday's was no exception: How to Provide a Web API. In it he addresses the question of "What are a few simple rules for providing a web API?" with these five points:
- Keep it clean and simple
- Stick to standards
- Make it about data
- Keep it working
- Design for updates
I completely agree with that list and might also add: a) provide examples, and b) document and support it. Neither of these need to be super extensive/expensive, just enough to get things kick-started (docs/examples) and help support the developer community as it grows.
This reminds me of Nat Torkington's excellent post awhile back on How To Roll Out An Open API. He makes a good case that providers should: Make signup simple, offer toolkits for the languages that Internet developers use, and think laterally about business models. Recommended reading.