Python design and style defaults

Personal, agent-maintained Python projects. Applies when writing new code or reviewing existing code against one of the topics below without an explicit "evaluate alternatives" request — pick the default, don't re-litigate from scratch each session. Deviating is fine when a case genuinely matches one of the named escalation paths — the point is to stop a fresh session/model from silently picking something different for no reason, not to forbid judgment calls.

Two topics were split out on 2026-08-31 and are separate installs: test-suite conventions are in python-testing-conventions, and the stdio-logging, tool-boundary and tool-docstring rules for MCP servers are in mcp-python-conventions. The split was measured before it was made — the pieces were checked against real requests to confirm each wins its own and none steals from the others.

This is design guidance, not tool config. Nothing here tells you which type checker or linter to install, or how to configure one — that belongs to whatever your repo uses to enforce its own standards (basedpyright, ruff, shellcheck/shfmt, dprint and pytest config, in this author's case). This skill is what to reference while writing code; tooling config is what a repo enforces once, at setup.