TRANSECT is a MATLAB toolbox developed during the PhD thesis “Relief dynamics of the Vosges through morphometric and cosmogenic nuclide analyses: a case of transient landscapes in a low-deformation context” by Bastien Mathieux. The TRANSECT toolbox provides a framework to build, analyse, and visualise transects perpendicular to a user-defined baseline in a Digital Elevation Model (DEM). The baseline can represent a drainage divide, river reach, valley axis, or other geomorphic feature. TRANSECT constructs connected paths perpendicular to the baseline using either geometric buffers or flow-routing along the topography. Each transect is stored in a structured object. The object supports flexible resampling, extraction of coordinates and elevations, pairing with spatial features, statistics computation, and visualisation. This alpha release provides the initial public version of the toolbox. The code is functional but remains under active development. TRANSECT relies on TopoToolbox (Schwanghart and Scherler, 2014) for DEM handling, flow routing, and coordinate transformations. Schwanghart, W., & Scherler, D. (2014). TopoToolbox 2: MATLAB-based software for topographic analysis and modeling in Earth surface sciences. Earth Surface Dynamics, 2, 1–7.