A measurement of the primary Lund jet plane density in inclusive jet production in proton-proton collisions is presented. The Lund jet plane, a representation of emissions inside jets, is extracted using iterative jet declustering techniques. The transverse momentum kT and the splitting angle ΔR of an emission relative to its emitter are measured at each step of the jet declustering process. The measurement is reported as a per-jet double-differential cross section in ln(kT/GeV) and ln(R/ΔR) for jets with transverse momentum pT> 700 GeV and rapidity |y|<1.7 with distance parameters R=0.4 and R=0.8. Only the charged particles of the jet are used, to achieve superior momentum and angular resolution. The differential cross section is corrected for acceptance, efficiency, and detector effects. We use 138 fb−1 of data collected by the CMS experiment at √s=13 TeV. The different regions of the Lund plane isolate specific physical effects, allowing for a factorized comparison to state-of-the-art Monte Carlo event generators and to analytical perturbative quantum chromodynamics calculations.