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Fettle is an experimental mutation testing tool for C#.


Fettle can mutate C# code that runs on the .NET Framework (Mono or .NET Core are not supported).

If your tests use NUnit 3, Fettle will use them by default (version 3.10 or higher recommended).

Or if you use another framework, or need to run them in a special way, then you can use a custom test runner command.

Getting Started

To start using Fettle, see the getting started guide.
To build from source, see the developer guide.


Fettle comes with some optimisations to make mutation testing faster:

More Info

If you're having problems running Fettle see the troubleshooting guide.
If you're still having issues feel free to get in touch on the gitter page or create an issue.

There's also a list of supported mutations.

Built With

Fettle relies on some awesome .NET projects which include:


This is an experimental project run within comparethemarket / BGL Group. If you are stuck, or keen to help, then please get in touch on the gitter page or open an issue.

Note that we have a code of conduct.


Oli Wennell did the initial work and is the project's maintainer.
Here's a list of the lovely people that have helped the project by contributing.


This project is licensed under the MIT License - see the LICENSE file for details


Thanks to:

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