I’m a firm fan of a design-first approach to building APIs, and advocate for it at every opportunity. Repeatedly. Design-first means that an API change starts in the OpenAPI description, gets reviewed and approved by the stakeholders, and then gets built afterwards.

I also live in the real world, where OpenAPI descriptions get generated from existing codebases, and engineering teams lack either the knowledge or the enthusiasm to modernise their processes. With a generated OpenAPI description, everything else that OpenAPI enables is likely to be disappointing, because the description only contains the information that was in the serverside code, and if you’re lucky some comment metadata. Enter OpenAPI Overlays, a way to describe alterations to an existing OpenAPI description that can be reapplied every time that description changes. Continue reading →