Users of your API will have to create code that can interact with it. To make it easier for them, you can provide an SDK that contains a reusable client code that fits the schema of your API. By providing the SDK, you can add client-side logic, such as validations and transformations, that can reduce the load from your API and help the developers that use your API to write their applications faster and with reduced errors. 

Swagger provides two nice tools that can help you generate the client code (or at least the stubs in it) from the OpenAPI definition file:

• Swagger Editor: A web editor that allows the editing of OpenAPI/Swagger definitions, visualizing them, and generating code from them.
• Swagger Codegen: A template-driven engine to generate documentation, API clients, and server stubs in different languages by parsing your OpenAPI/Swagger definition. This is usually used as a CLI tool that can be incorporated and then generate the client build automatically.