We introduce an open-source fiber laser and amplifier design toolbox written in Matlab. A graphical user in-terface provides access to analysis functions for both core- and cladding-pumped, erbium- and ytterbium-dopedber lasers and amplifiers. These functions use a combination of analytical calculations and numerical simulation to predict performance and generate output plots. The finite-difference time-domain (FDTD) numerical simu-lator used implements a Lax-Wendro approach that is second-order accurate in both time and space for fast convergence. The simulator solves general active fiber wave propagation and rate equations, allowing modeling of other dopants, other system configurations, and dynamic signals. The toolbox calculations show good agreement with published results and with our own experiments.