APIs are promises written in code—contracts between software systems that make it possible for strangers to build on each other's work without ever meeting.
REST isn't a protocol—it's a philosophy. Resources have addresses. Actions have verbs. State lives in the message. Understanding why these constraints exist makes the difference between APIs that work and APIs that fight you.
REST is a bet: organize around resources, use HTTP correctly, and developers will guess how your API works before reading your docs.
Every API request asks the same question: who are you, and should I trust you? Here's how authentication answers it—from simple API keys to OAuth's elegant delegation.
Rate limiting is the bouncer at your API's door—it decides who gets in, how often, and what happens when someone tries to cut the line.
Versioning isn't about URL schemes—it's about managing trust. Learn when breaking changes are worth the broken promises, and how to evolve your API without losing the developers who depend on it.
OpenAPI makes your API documentation impossible to lie—the spec and the truth become the same thing, enabling tooling that actually works.
Webhooks flip the fundamental question of networked systems: instead of asking 'has anything changed?', you get told the moment something does.
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