The OpenAPI specification is open — really open. From the beginning, the specification allowed specification extensions (properties prefixed by "x-" ) just about anywhere. This feature adds extensibility, yes, but also great power. At Apiture, we embrace the API First design process and use specification extensions to augment our APIs, automate much of our build pipeline, and improve our developer experience. Extensions allow us to capture semantic information about the APIs in a structured way that tools can analyze and process. From our raw OpenAPI source files (with extensions), we generate secondary and even tertiary OpenAPI source files, which we then feed into code generators (openapi-generator and others) and API documentation generators. You’ll see how our OpenAPI annotations tool processes an input OpenAPI definition to generate an output OpenAPI definition with augmented and uniform descriptions strings for schema versioning, deprecation warnings, enhanced enumeration documentation, one-way data encryption, schema resolution and cleansing, and more. You too can use extensions to create better API definitions!