Renaming an API field is the most dangerous breaking change — diff the spec in CI
Franc0Fernand0 · x · 2026-09-25
Franco Fernando continues his API design series in issue 192 of the Polymathic Engineer. Core point: a published API is a running service, not a library — one field rename can break every client that parsed the old name on deploy, and such changes look harmless in code review.
The fix: describe the API layout in an OpenAPI spec as a single machine-readable source of truth, diff the spec in CI, and fail the build on breaking changes. The spec also enables code generation, live traffic validation, examples/mocking, and versioning. "An accidental rename should break a build, not an integration."
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