The climate crisis requires developing countries to urgently decarbonize energy systems and mobilize finance while balancing competing priorities such as economic growth, energy security, environmental sustainability, and social development. However, many developing countries face challenges in developing long-term energy planning strategies, including limited capacity and reliance on external consultants. To address these issues, 21 international organizations and research institutions have developed five strategic principles for energy planning: national ownership, coherence and inclusivity, human capacity development, analysis robustness, and transparency and accessibility of data and tools. This paper discusses joint efforts to promote and apply these principles using science-based evidence and analytical modelling tools, such as the Open Source Energy Modelling System (OSeMOSYS) and the power system IRENA FlexTool. These tools are part of a suite of emerging modelling tools to support climate-compatible development policies and have been included in accessible teaching material, online courses, summer schools, and capacity development programs.