GRB 230812B broad-band spectral energy distribution (solid red and green lines) modelling for two different time intervals, including early-time X-ray and high-energy afterglow data (25–250 s) and late-time afterglow optical and X-ray data at 30 ks. The afterglow emission is produced in the synchrotron and SSC external forward shock scenario. Observed data points (filled circles) and upper limits (arrows) from multiple instruments spanning the early to late afterglow phases are displayed. The energy bands used in the analysis are indicated in the legend: optical (r′; magenta), XRT (0.3–10 keV; purple), GBM (40–400 keV; green), and LAT (0.1–100 GeV; cyan). Details of the modelling and derived parameters are provided in Sect. 4.