A Python package for flavour physics phenomenology in the Standard Model and beyond

flavio is a Python 3 package to compute predictions for hundreds of observables in flavour physics, both in the Standard Model and for arbitrary new physics effects (parametrized as Wilson coefficients of dimension-6 operators). Additional features are in development.

Easy to install

Thanks to Python, no compilation is necessary, even when you make changes to the code.

Easy to customize

By modifying simple text files, you can change input parameters or choose between different implementations, e.g. for hadronic form factors.


Using iPython, you can evaluate observables in an interactive session (similar to Mathematica).

Featured processes

  • $B^0$, $B_s$, and $K^0$ mixing
  • $B\to K^{(*)}\mu^+\mu^-$ and other exclusive rare $B$ decays
  • Inclusive decays $B\to X_{s,d}\gamma$
  • Lepton flavour violating $B$ decays
  • $B\to D^{(*)}\tau\nu$ and other tree-level $B$ decays
  • $K\to \ell\nu$, $K\to \pi\ell\nu$, and $K\to \pi\nu\bar\nu$ decays

License & disclaimer

The code is released under the MIT license. As such, it is provided “as is” without any warranty.

flavio is still in beta phase, so there might still be bugs. Please double-check with a second tool (check out EOS) if you think you have discovered new physics.

If you use flavio in a project, please cite:


The theme of this web site is based on devAid by Xiaoying Riley, licensed under CC BY 3.0.


Main developer: David Straub

Please file bug reports and make feature requests over at Github