[Co-presented with Mike Kistler, Architect for SDK Generation for the Watson Client Libraries] The OpenAPI Specification is emerging as the leading standard for describing REST APIs. A key factor in the popularity of OpenAPI is the broad array of open source tools that it enables that create, manipulate, and publish documentation and code from OpenAPI descriptions. In this talk, we describe a configurable and extensible open source linter for OpenAPI that we are using to solve API code generation problems at IBM and Google. Our linter is based on Gnostic, an open source framework for working with API descriptions that was developed at Google and is available on GitHub. OpenAPI itself is language-agnostic and is being used to generate code in a large set of popular programming languages. This generated code includes both server-side "stubs" and client libraries that are sometimes called software development kits (SDKs). IBM has begun to employ code generation for the Watson Developer Cloud SDKs and other companies are doing similar things, including Google, which generates client libraries from Google-specific API description formats. These teams have found that the quality of SDKs generated from API descriptions depends heavily on the quality of the descriptions. This goes far beyond mere syntactic compliance with a specification -- it involves proper API design, naming, and adherence to organization-wide design patterns. To address this, many companies have created API design guides. Some companies, such as Google and Microsoft, have published their API design guides externally, while others like IBM have kept theirs as internal documents. But to this point, verifying compliance with an API design guide has largely been a manual task. What is needed, we believe, is a configurable and extensible linter to check OpenAPI descriptions for conformance with rules derived from API design guides.