  Giant planet evolution models play a crucial role in interpreting
observations and constraining formation pathways. However, the simulations can
be slow or prohibitively difficult. To address this issue, we calculate a large
suite of giant planet evolution models using a state-of-the-art planetary
evolution code. Using these data, we create the python program planetsynth that
generates synthetic cooling tracks by interpolation. Given the planetary mass,
bulk & atmospheric metallicity, and incident stellar irradiation, the program
calculates how the planetary radius, luminosity, effective temperature, and
surface gravity evolve with time. We demonstrate the capabilities of our models
by inferring time-dependent mass-radius diagrams, estimating the metallicities
from mass-radius measurements, and by showing how atmospheric measurements can
further constrain the planetary bulk composition. We also estimate the mass and
metallicity of the young giant planet 51 Eri b from its observed luminosity.
Synthetic evolution tracks have many applications, and we suggest that they are
valuable for both theoretical and observational investigations into the nature
of giant planets.
