Purpose:To measure and simulate well‐defined electron spectra using a linear accelerator and a permanent‐magnetic wide‐angle spectrometer to test the performance of a novel reconstruction algorithm for retrieval of unknown electron‐sources, in view of application to diagnostics of laser‐driven particle acceleration.Methods:Six electron energies (6, 9, 12, 15, 18 and 21 MeV, 40cm × 40cm field‐size) delivered by a Siemens Oncor linear accelerator were recorded using a permanent‐magnetic wide‐angle electron spectrometer (150mT) with a one dimensional slit (0.2mm × 5cm). Two dimensional maps representing beam‐energy and entrance‐position along the slit were measured using different scintillating screens, read by an online CMOS detector of high resolution (0.048mm × 0.048mm pixels) and large field of view (5cm × 10cm). Measured energy‐slit position maps were compared to forward FLUKA simulations of electron transport through the spectrometer, starting from IAEA phase‐spaces of the accelerator. The latter ones were validated against measured depth‐dose and lateral profiles in water. Agreement of forward simulation and measurement was quantified in terms of position and shape of the signal distribution on the detector.Results:Measured depth‐dose distributions and lateral profiles in the water phantom showed good agreement with forward simulations of IAEA phase‐spaces, thus supporting usage of this simulation source in the study. Measured energy‐slit position maps and those obtained by forward Monte‐Carlo simulations showed satisfactory agreement in shape and position.Conclusion:Well‐defined electron beams of known energy and shape will provide an ideal scenario to study the performance of a novel reconstruction algorithm using measured and simulated signal. Future work will increase the stability and convergence of the reconstruction‐algorithm for unknown electron sources, towards final application to the electrons which drive the interaction of TW‐class laser pulses with nanometer thin target foils to accelerate protons and ions to multi‐MeV kinetic energy.Cluster of Excellence of the German Research Foundation (DFG) “Munich‐Centre for Advanced Photonics”