A server in a content delivery network (CDN) can examine API traffic and extract therefrom content that can be optimized before it is served to a client. The server can apply content location instructions to a given API message to find such content therein. Upon finding an instance of such content, the server can verify the identity of the content by applying a set of content verification instructions. If verification succeeds, the server can retrieve an optimized version of the identified content and swap it into the API message for the original version. If an optimized version is not available, the server can initiate an optimization process so that next time the optimized version will be available. In some embodiments, an analysis service can assist by observing traffic from an API endpoint over time, detecting the format of API messages and producing the content location and verification instructions.