Network functions virtualization (NFV) opens up a new ability of network enablement through agile network DevOps to design, develop, and test new services and to provide ongoing updates of existing services. This paper proposes a tool and methodology to aid the NFV designer to rapidly design and onboard new services and applications. Although the main focus is on the service design and onboarding, we provide the relation with other aspects such as management and orchestration, and service assurance of a complete lifecycle for network service. The proposed tool and methodology is called VNF Onboarding Automation Tool (VOAT). The prototype implementation is discussed as well as various use cases where VOAT has been used. With VOAT, an automated service design and onboarding can be efficiently achieved, hence reducing significantly the timeframe for deploying new services in telco cloud-based environment.