The growing intersection between climate change and human mobility argues that migration, displacement, and immobility are increasingly shaped by both sudden-onset and slow-onset climate hazards, alongside underlying social and governance vulnerabilities. Most climate-related mobility occurs within national borders and carries considerable implications for health, livelihoods, and urban systems. Global frameworks such as the Global Compact for Migration and the UN Framework Convention on Climate Change have begun to acknowledge these dynamics; however, a major adaptation gap is identified at the national level. Climate-related mobility is often referenced in national adaptation plans, but coherent implementation strategies, coordination mechanisms, and monitoring systems remain underdeveloped. To address this adaptation gap, this Personal View proposes a structured diagnostic assessment tool to evaluate how effectively mobility is integrated into national adaptation plans across domains, including risk assessment, governance, legal preparedness, financing, and monitoring and evaluation. Rather than ranking countries, the tool supports context-sensitive analysis, strengthens institutional readiness, and facilitates cross-country learning. This paper calls for a shift towards anticipatory, rights-based adaptation planning that recognises mobility as both a potential risk and an adaptive strategy in response to climate change.