The Parallel Checker (formerly also called "HSR Parallel Checker") is a static analyzer for Visual Studio® and VS Code that detects data races, deadlocks and other concurrency issues in C#.


  • Static: Finds issues that are hard to identify through tests.
  • Fast: Takes only a few seconds, even for large projects.
  • Precise: Detects real issues that can occur indeed at runtime.
  • Interactive: Highlights issues while coding in Visual Studio® or VS Code IDE.

NEW: May 2021: Version 1.9 for C# 9 released!

An updated version of Parallel Checker has been released that supports the latest Visual Studio 2019 Preview and C#.

Try the checker online!

You can now experiment with the Parallel Checker directly on the website: Try it!. The web version is enabled by .NET Mono WebAssembly cross-compilation.

NuGet Analyzer for VS Code

The Parallel Checker is now also available as NuGet package, such that it can be conveniently used in the VS Code integrated development environment.

Academic Publication

The checker algorithm, design and implementation is described in an academic publication:

  • L. Bläser. Practical Detection of Concurrency Issues at Coding Time. International Symposium on Software Testing and Analysis (ISSTA) 2018, Amsterdam, The Netherlands, In ACM Digital Library, July 2018.

Notice: Microsoft, Visual Studio, and Visual Basic are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries.

All trademarks, trade names etc. are the property of their respective owners.

OST, Parallel Checker, HSR, Concurrency Lab, and the contributors DO NOT have any affiliation with any mentioned trademark holders.