Apr 22
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API design principles explained — resource-oriented design, the stability hierarchy, why leaking your database schema through your API surface creates expensive migration debt, and how to design errors as part of the contract. A 3-day database rename took 4 months — because 14 clients depended on field names copied straight from the schema. Runtime Ethos Day 13 shows you why API design is contract design, and what that means in practice. Most engineers design APIs for the database: field names from columns, endpoints shaped around tables, responses built for storage not for use. This video breaks down the principles that make an API a contract you can actually keep — resource-oriented design, the stability hierarchy, versioning as a last resort, and the single rule that would have saved that 4-month migration. Covers: the cost of leaking your database schema through the API surface, the mapping layer pattern, why resources represent business concepts not tables, what makes certain API changes more expensive than others, and how to design errors as part of the contract. Follow for 90 days of engineering mental models → @RuntimeEthos ◀ Previous: Day 12 — Service Boundaries https://www.youtube.com/watch?v=TtoBlIxtdcQ ▶ Next: Day 14 — Event Driven Systems (coming soon) #apidesign #backendengineering #runtimeethos