The use of vibration energy harvesting systems for supplying energy to wireless sensor nodes is becoming increasingly popular. This paper presents a magnetically sprung vibration energy harvester that has a broadband response and is tunable. The system comprises three annular magnets longitudinally arranged along a shaft, resulting in a nonlinear hardening suspension and consequential "jump" phenomenon characteristic. This paper presents and validates a toolbox that can be used to develop such systems using a time step model and prototype. It comprises accurate models of the magnetic suspension force and electromagnetic coupling coefficient, which links the mechanical and electrical domains. The system is compared with those in the literature using power density and effectiveness metrics. The nonoptimized prototype has an average power density of 600 W.m(-3) and is comparable to those in the literature.