Developers are users too.
If other businesses build on your API, it's a product. Its users are developers, and their experience decides whether they succeed.
Clear docs
Accurate, with examples. Updated with every change.
Stable versions
Changes announced early. Old versions retired gently.
Helpful errors
Messages that say what went wrong and how to fix it.
Fast first success
A sandbox and a quick-start. Measure time to first working call.
Treat your API like a product.