OpenCover

OpenCover is an open-source code coverage tool for .NET applications. It works by attaching to a running .NET process using the CLR Profiling API to monitor executed code during test runs, thereby collecting coverage data. OpenCover can report coverage at the level of assemblies, classes, methods, and individual lines, and supports including or excluding code through filters based on assembly name, namespace, or attributes.

OpenCover outputs its findings in an XML format known as the OpenCover format. The standard workflow is to run OpenCover with a test runner (for example MSTest, NUnit, or xUnit) as the target, so that tests execute under the profiler and coverage data is collected. The resulting XML can be consumed by reporting tools such as ReportGenerator to produce human-readable HTML reports, charts, or other formats. OpenCover integrates into continuous integration workflows and is commonly used with Windows-based .NET projects.

OpenCover is designed for Windows and primarily supports the .NET Framework; there are community efforts and forks that extended compatibility with .NET Core and newer runtimes. It remains one of several tool options for .NET code coverage, alongside alternatives such as Coverlet and dotCover.