  Mata is a well-engineered automata library written in C++ that offers a
unique combination of speed and simplicity. It is meant to serve in
applications such as string constraint solving and reasoning about regular
expressions, and as a~reference implementation of automata algorithms. Besides
basic algorithms for (non)deterministic automata, it implements a fast
simulation reduction and antichain-based language inclusion checking. The
simplicity allows a straightforward access to the low-level structures, making
it relatively easy to extend and modify. Besides the C++ API, the library also
implements a Python binding. The library comes with a large benchmark of
automata problems collected from relevant applications such as string
constraint solving, regular model checking, and reasoning about regular
expressions. We show that Mata is on this benchmark significantly faster than
all libraries from a wide range of automata libraries we collected. Its
usefulness in string constraint solving is demonstrated by the string solver
Z3-Noodler, which is based on Mata and outperforms the state of the art in
string constraint solving on many standard benchmarks.
