Hector is developed as an object-oriented, open-source, simple climate-carbon cycle model. The default model consists of a well-mixed atmosphere, a land surface (vegetation, detritus, soil) with the option to specify multiple biomes, and an ocean consisting of a high and low latitude surface box, an intermediate and a deep box. Carbon emissions, along with numerous other gases, pollutants, and aerosols are inputs into Hector from which radiative forcing, atmospheric temperature, and pCO2 concentrations are calculated. Importantly, model components can be swapped in and out dynamically, so different (e.g.) oceans can be easily implemented. Hector currently reproduces the large scale trends in the global climate from observations and the CMIP5 output, from 1750 to 2300. A unique feature of Hector is the interactive carbon chemistry within the surface ocean boxes. The inorganic carbon cycle is directly calculated from surface ocean temperature, which is a function of global temperature, salinity, and the delta carbon between the ocean and atmosphere. This allows for Hector to actively calculate the air-sea fluxes of CO2, pH, and calcium carbonate saturations in the surface oceans. Hector accurately produces the large negative trends in pH and saturations under future warming scenarios.