Ask HN: What are best practices to building a developer experience?

We're opening up integrations on our platform so developers can build on top of us. What matters to you as a developer when interacting with a 3rd party API? Would appreciate any pointers to good developer experiences (I like Slack and Stripe) and how to think about implementing them

Top of mind is: - Comprehensive documentation - Interactive APIs - Easy to test - Easy to get keys, register webhooks, etc to setup OAuth - Fast approval if needed - Stats on your API usage