Suitability of TOI-2406 b for transmission spectroscopy studies. Top panel: complete sample of known transiting exoplanets. Bottom panel: focuses on the coolest ones amenable to study. TOI-2406 b, highlighted in both panels, is among the most accessible cool planets for atmospheric studies. Planets are colour-coded by the radius bins of Kempton et al. (2018). Filled circles indicate planets with mass measurements, while outlined circles indicate those with masses estimated from empirical mass-radius relations. Some highly accessible planets smaller than Neptune are named and highlighted with black outlines in the bottom panel.