Establish secure default configurations in project metadata files to prevent accidental publishing and ensure proper version constraints. This is particularly important for private packages and build system configurations. Key practices: 1. Add the "Private :: Do Not Upload" classifier for non-public packages: ```toml [project] classifiers = [ "Private :: Do Not Upload", # Other classifiers... ] ``` 2. Use appropriate version constraints in build system requirements: ```toml [build-system] # Prefer narrow version ranges for build backends requires = ["uv>=0.4.18,<0.5"] ``` 3. Validate completeness of required configuration fields: - Ensure project.name is specified - Include explicit version information - Define clear build system requirements This approach helps prevent accidental package uploads to public repositories and ensures reproducible builds through proper version constraints.