GIFTS is a 6U CubeSat designed to detect and localise gamma-ray bursts (GRBs). Its main goal is to improve the sky coverage of existing GRB observatories and contribute to the search of electromagnetic counterparts to gravitational-wave events. GIFTS will use six CeBr \( _3 \) scintillator detectors oriented at different angles to localise GRBs based on the difference in the observed count rates. Each detector employs an array of 24 SiPMs for scintillator readout. A full-size prototype of one GIFTS detector was built and tested with gamma rays with energies ranging from 31 keV to 1.3 MeV. It showed an energy resolution of 5.4% at 662 keV. Monte-Carlo simulations were used to estimate the GRB detection and localisation performance of the full instrument. GIFTS was able to detect about 50% of the GRBs from the Fermi GBM catalogue, provided they were not occulted by Earth. Assuming a 60% duty factor for GRB observations, GIFTS is expected to detect about 80 GRBs/year including 12 short GRBs/year. For 90% of the detected GRBs with positive elevations, the true localisation error is less than 32 \( ^{\circ } \) . The localisation error is mainly defined by statistical fluctuations in the observed count rates and becomes smaller for brighter events. Systematic localisation errors are expected to depend mainly on the accuracy of the instrument response model used by the localisation procedure. GIFTS is under development and expected to be launch ready for the next gravitational-wave observing run (O5).
