The NEMO (NEutral beam MOdelling) code for simulating the neutral beam ionization during Neutral Beam Injection (NBI) in tokamak plasmas has been developed for its implementation in integrated modelling frameworks and is presented. Integrated modelling of fusion plasmas is becoming increasingly important, both for preparation and analysis of experiments in large devices. Moreover, it should play a crucial role for the design of future fusion reactors. In a modern context, integrated modelling requires codes that are: (i) flexible in terms of their interfaces, i.e. can be adapted for different simulation environments, (ii) machine independent; i.e. they should not contain hard coded information on a particular device to be simulated; (iii) optimised for speed of execution, (iv) verified and validated. The NEMO code has been specially designed to meet these requirements. The code is based on the physics concept outlined in [1] and is a completely modular program: it works with any input NBI geometry and can be coupled to any external Fokker-Planck calculation for evaluating the distribution function of the injected species, i.e. it can provide source terms for both Monte Carlo codes and codes using finite difference/elements methods. The NEMO code has already been integrated with the CRONOS integrated modelling suite [2] and the European Integrated Tokamak Modelling Task Force (ITM-TF) [3]. The basics of the code are described in this paper along with an illustration of its integration in the ITM-TF simulation platform. A crucial aspect is the verification of the code, the results of benchmarks carried out with other NBI codes for JET and ITER discharges are thereby presented.