NbodyGradient computes gradients of N-body integrations for Newtonian gravity and arbitrary N-body hierarchies. Developed for transit-timing analyses and written in Julia, NbodyGradient gives derivatives of the transit times with respect to the initial conditions, either masses and Cartesian coordinates/velocities or orbital elements.

Photodynamics.jl computes synthetic transit light curves for multi-planet systems by coupling the N-body integrator NbodyGradient.jl (ascl:2503.002) with the analytic transit and limb-darkening model Limbdark.jl (ascl:2511.014). The software produces time-integrated fluxes and analytic derivatives with respect to dynamical and photometric parameters, enabling gradient-based inference of systems exhibiting transit-timing variations. Implemented in Julia, Photodynamics.jl supports efficient fitting of high-dimensional photodynamical models using modern probabilistic sampling methods.