MSMBuilder is an open source software package for automating the construction and analysis of Markov state models (MSMs). It is primarily written in the python programming language with C extensions for the most time consuming routines.

MSMs are a powerful means of modeling the structure and dynamics of molecular systems, like proteins. An MSM is essentially a map of the conformational space a molecule explores. Such models consist of a set of states and a matrix of transition probabilities (or, equivalently, transition rates) between each pair of states. Intuitively, the states in an MSM can be thought of as corresponding to local minima in the free energy landscape that ultimately determines a molecule’s structure and dynamics.

MSMBuilder includes tools for
- Constructing an MSM from a set of computer simulations (typically molecular dynamics simulations in standard formats like xtc, dcd, and pdb)
- Validating statistical properties of MSMs
- Mimicking various experimental protocols to allow a quantitative comparison with experiments
- Driving efficient simulations via adaptive sampling (which decides where new simulations should be run to minimize statistical uncertainty in a model)

For more information, including the latest releases, see our website at

MSMBuilder.org