8 API Design Mistakes That Will Haunt You in Production

APIs are permanent. That sounds dramatic until you've spent three weeks coordinating a breaking change across fourteen client teams while keeping the old endpoint alive in a compatibility shim nobody wants to maintain. Bad code can be refactored quietly. A bad API contract is a public debt that compounds interest every quarter. Here are eight patterns drawn from designs that looked reasonable at the time, shipped to production, and then caused real pain. Mistake 1: Not Versioning From Day One The argument against early versioning sounds rational — you don't know what will change yet. The problem is that "later" arrives the moment a single external client goes to production. At that point, adding versioning requires a migration, not just a decision. URL path versioning (/v1/users, /v2/users) is the most explicit approach and the right default for most teams. It's easy to route at the infrastructure level and visible in any log file. Stripe uses it for good reason: its clarity is a signi