The Cost of a Promise

That’s why API design deserves far more care than it usually receives.

Good APIs are boring in the best way. They are predictable, explicit, and unsurprising. They avoid clever shortcuts in favor of clarity. Consumers should not need to guess what an endpoint does or how a field behaves under edge conditions.

One of the hardest parts of API design is restraint. Every field added is a commitment. Every optional parameter increases the surface area for bugs. Flexibility feels generous in the moment but becomes expensive over time. Strong APIs say “no” more often than “yes.”

Consistency matters more than perfection. Naming conventions, error formats, pagination strategies—these things compound. Inconsistent APIs force consumers to write special-case logic, which is a hidden tax on every integration.

Versioning is another area where theory and practice diverge. In reality, versioning is less about URLs and more about change management. Backward compatibility, deprecation timelines, and communication matter more than whether you use /v1.

APIs should also be designed with failure in mind. Clear error messages, meaningful status codes, and idempotent operations make systems more resilient. Consumers will misuse your API. it’s not a matter of if, but when.

At their best, APIs reflect thoughtful system boundaries. They expose intent, not internals. When done right, they allow teams to move independently without stepping on each other. When done poorly, they become tight coupling disguised as a service.