An analysis tool for Python that blurs the line between testing and type systems.

THE LATEST NEWS:
Check out the new crosshair cover command which finds inputs to get you code coverage.

If you have a function with type annotations and add a contract in a supported syntax, CrossHair will attempt to find counterexamples for you:

CrossHair works by repeatedly calling your functions with symbolic inputs. It uses an SMT solver (a kind of theorem prover) to explore viable execution paths and find counterexamples for you. This is not a new idea; a Python approach was first described in this paper. However, to my knowledge, CrossHair is the most complete implementation: it supports symbolic lists, dictionaries, sets, and custom classes.

Try CrossHair right now, in your browser, at crosshair-web.org!

CrossHair has IDE integrations for VS Code, PyCharm, and more.

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• Introduction
• Get Started
• The Details: Contracts
• The Details: cover
• The Details: diffbehavior
• Kinds of Contracts
• Hints for Your Classes
• IDE Integrations
• Case Studies
• Limitations
• Plugins
• How Does It Work?
• How Can I Help?
• Related Work
• Contributing
• Changelog