The crisis caused by the COVID-19 has awakened the fear of forgetting the fight against Climate Change coming up with a number of initiatives demanding to accelerate the European Green Deal, as the best way out of the crisis. Offshore renewable energy sources, including offshore wind, wave power and tidal streams, might play a crucial role in meeting low-carbon energy scenarios, which is one of the six key principles of the Green Recovery, contributing at the same time to economic growth and job creation. However, continuous cost reduction is needed to achieve more efficient and competitive technologies in comparison to other energy sources. Design tools can help to accelerate cost reduction in early stages of technology development or deployment project planning. This article shows some examples of design tools developed within four European funded R&D projects: • DTOcean and DTOceanPlus provide advanced design tools for ocean energy systems innovation, development and deployment • LIFES50+ proves cost effective technology for floating substructures for 10MW wind turbines at water depths greater than 50 m • OPERA collects, analyses and shares open-sea operating data and experience to validate and de-risk several industrial innovations for wave energy The design tools presented in this article cover different stages of technology or project development: • Multi-physics numerical modelling tools for the design of floating offshore wind turbines • Decision-making tools during the planning phase of offshore wind or ocean energy farms • Structured innovation and stage gate tools for the evaluation of innovations for offshore renewables at early stages of development The reader will be able to find out references to useful open source tools and public documents produced by these projects. Keywords: design tools, offshore wind, wave power, tidal energy, numerical modelling, structured innovation, deployment project planning