We introduce a web application (CatApp) for looking up calculated reaction and activation energies for elementary coupling reactions occurring on metal surfaces. It provides access to reaction and activation energies for all reactions involving C-C, C-H, C-O, O-O, O-H, N-N, C-N, O-N, N-H splittingSolid catalysts form the backbone of the chemical industry and the hydrocarbon-based energy sector. Most catalysts and processes today are highly optimized, but there is still considerable room for improvements in reactivity and selectivity that would lower energy consumption and waste production. In addition there are tremendous challenges to catalysis science and engineering in developing a sustainable energy solutions. The ability to store solar energy as a fuel calls for new catalysts and so does the development of a sustainable chemical industry based on biomass and other non-fossil building blocks.The development of new catalysts could be accelerated significantly if we had access to systematic data for activation energies of elementary surface reactions. Once the key parameters determining the activity or selectivity of a certain process has been established though experiments or calculations, such a database would enable searches for new catalyst leads. Ideally, data would come from detailed, systematic experiments, but it is in general not possible to find such data. Electronic structure calculations provide a powerful alternative. The accuracy is not such that detailed predictions of absolute rates of elementary reaction steps can be made, but for classes of interesting catalysts (transition metals) it is possible to create systematic data with sufficient accuracy to predict trends in reactivity. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] In the present paper, we introduce such a set of calculated reaction energies and activation energies for a large number of elementary surface reactions on a series of metal single crystal surfaces including surfaces with defects such as steps. We will also introduce a simple web application (CatApp) that can be downloaded to access these data.