Geomagnetic observatories are dedicated to the long-term monitoring of the Earth's magnetic field. Their time series contain information mainly about the Earth's core and the near-Earth space environment. MOSFiT accesses a global database with the most recent observatory data and allows us to separate the information about the Earth's core. At the same time, it allows for an efficient check of the data quality. We present the code, validate it and explain its usage.