The requirement to make a climate declaration in connection with the construction of a new building came on 1 January 2022, which means that the client is obliged to declare a climate footprint. At present, there are no limit values or guidelines on how large a climate impact and building may have, but in the future this will be introduced. The purpose of today's requirements for documentation is an increased knowledge of the climate issue and that the construction industry should work more sustainably. Climate declaration is a completely new part of the construction process and currently there are a number of different tools for producing a climate declaration. However, there is a lot to investigate regarding to which functions and tools are most effective for the future climate declaration.  Sweco has started to develop the tool C3, which calculates the climate impact of building components in a 3D model, as well as comparing different materials in carbon dioxide emissions and cost to facilitate calculation based on climate impact. It would be beneficial if the climate impact-based calculation in C3 could be combined with climate declarations to make work more efficient, and this issue has formed the basis for the report.  This thesis examines how three existing tools currently work and then evaluates this in relation to future climate declaration tools. The study aims to determine which functions are desirable to implement in a future climate declaration tool, such as C3.  The test execution, which was based on a BIM model, together with a literature study and interviews, has resulted in the required functions in a climate declaration tool being: a clear interface with high user-friendliness, smart and automated functions and integration of digital tools. The results show that these functions together will contribute to more efficient and precise climate declaration work. The survey has also shown that a prerequisite for climate declarations to work in the industry is that the legal requirement that exists today is developed and, above all, clarified.