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APL photonics 8(3), 036114 (2023). doi:10.1063/5.0135252, Nonlinear optical frequency conversion is of fundamentalimportance in photonics and underpins countless ofits applications: Sum- and difference-frequency generationin media with quadratic nonlinearity permit reachingotherwise inaccessible wavelength regimes and the dramaticeffect of supercontinuum generation through cubicnonlinearities has resulted in the synthesis of broadbandmulti-octave spanning spectra, much beyond what can bedirectly achieved with laser gain media. Chip-integratedwaveguides permit to leverage both, quadratic and cubiceffects at the same time, creating unprecedented opportunitiesfor multi-octave spanning spectra, across the entiretransparency window of a nonlinear material. Designingsuch waveguides often relies on numeric modelingof the underlying nonlinear processes, which, however,becomes exceedingly challenging when multiple and cascadingnonlinear processes are involved. Here, to addressthis challenge, we report on a novel numeric simulationtool for mixed and cascaded nonlinearities that uses antialiasingstrategies to avoid spurious light resulting froma finite simulation bandwidth. A dedicated 5th-order interactionpicture Runge-Kutta solver with adaptive stepsizepermits efficient numeric simulation, as required fordesign parameter studies. Importantly, the simulation resultsare shown to quantitatively agree with experimentaldata and the simulation tool is made available as an opensourcePython package (PyChi)., Published by AIP Publishing, Melville, NY