The format that I like to use for bug reports (that I write myself, and that I like to receive) is as follows:
- Summary/title (one-line at most)
- Steps to reproduce
- Expected behavior
- Actual behavior
Explicitly mentioning the expected and the actual behavior is useful to avoid any assumptions about what is expected behavior.
Optionally, provide context:
- OS version
- Interpreter version
- Package manager version
- Stack trace (if regarding a crash)