This paper describes the design and implementation of the open-source tool $$\textsc {Coyote} $$ C O Y O T E for testing concurrent programs written in the $$\textsc {C}{} \texttt {\#} $$ C # language. $$\textsc {Coyote} $$ C O Y O T E provides algorithmic capabilities to explore the state-space of interleavings of a concurrent program, with deterministic repro for any bug that it finds. $$\textsc {Coyote} $$ C O Y O T E encapsulates multiple ideas from the research community to offer state-of-the-art testing for $$\textsc {C}{} \texttt {\#} $$ C # programs, as well as an efficiently engineered implementation that has been shown robust enough to support industrial use.