Purpose: Assessment of climate change risks and vulnerability is essential in order to inform and implement appropriate adaptation strategies. Disastrous effects of extreme weather events such as the heat waves across Europe in 2003 highlight the adaptation imperative. Regional spatial planning and urban design can help to reduce the vulnerability of communities to these risks. The purpose of this paper is to report on the development of an assessment tool, which highlights climate change risks and vulnerabilities in urban areas, and the results of pilot and user testing with the Green and Blue Space Adaptation for Urban Areas and Eco Towns (GRaBS) project partners. Design/methodology/approach: The tool follows the principles of an online public participation GIS, and is built using the Google Maps Interface. The approach is based on a risk framework, focusing on the three elements; hazard, vulnerability and exposure. Thus, the assessment tool assesses vulnerability of population and infrastructure in urban areas to climate change impacts (in particular flooding and heat stress). It also enables spatially relating patterns of vulnerability with risk where data are available. Findings: A key finding of the project has been the need to break down silos between departments in order to build an evidence base for decision makers for adaptation plans and strategies. The tool is considered to be an excellent means of raising awareness, and the results of the pilot study confirm the assessment tool is seen as innovative, cost effective, intuitive and simple to use and navigate. Furthermore, by helping to visualise vulnerability of urban areas it may be useful in supporting planning of both emergency responses and long-term land use changes. Research limitations/implications: The tool is limited by the availability of geospatial data and information, which has implications for the types of outputs the tool can produce. Practical implications: The tool has been implemented in all of the case study partner areas, which will be affected to a greater or lesser extent by a range of climate change impacts requiring responses, depending on the severity and likelihood of the hazard, vulnerability, and exposure. The methodological approach adopted in the project has to take account of this important issue. Originality/value: The tool brings together diverse data and information from a large number of European partners, and provides users with an understanding of climate change issues, many of whom may not have been familiar with the topic at the outset. The tool delivers GIS data and analysis functions on the web through the internet, widening the possibilities for participation in climate change adaptation planning. © Emerald Group Publishing Limited.