We should encourage offline development as much as possible. This ensures that endpoints are not overburdened and that users are not testing in production. If SDK's for a given api are produced, they should also include mock responses. This mock setting should be configurable in the SDK and allow a developer to 'flip a switch' and ping consistent and static end points as needed. This reduces latency for the developer and also provides a clean set of data from which tests can be run.