  The Adaptive Optics (AO) performance significantly depends on the available
Natural Guide Stars (NGSs) and a wide range of atmospheric conditions (seeing,
Cn2, windspeed,...). In order to be able to easily predict the AO performance,
we have developed a fast algorithm - called TIPTOP - producing the expected AO
Point Spread Function (PSF) for any of the existing AO observing modes (SCAO,
LTAO, MCAO, GLAO), and any atmospheric conditions. This TIPTOP tool takes its
roots in an analytical approach, where the simulations are done in the Fourier
domain. This allows to reach a very fast computation time (few seconds per
PSF), and efficiently explore the wide parameter space. TIPTOP has been
developed in Python, taking advantage of previous work developed in different
languages, and unifying them in a single framework. The TIPTOP app is available
on GitHub at: https://github.com/FabioRossiArcetri/TIPTOP, and will serve as
one of the bricks for the ELT Exposure Time Calculator.
