uv tool install builds on the system Python

EDIT: pacman’s python has since moved to 3.14.8, and b2 still runs.

uv tool install builds the tool environment against the system Python unless a uv-managed Python is already installed. I moved the Backblaze b2 CLI off pipx so a pacman python bump could not break the backup push, and it changed nothing:

$ cat ~/.local/share/uv/tools/b2/pyvenv.cfg
home = /usr/bin
implementation = CPython
uv = 0.12.13
version_info = 3.14.7
include-system-site-packages = false

home = /usr/bin is pacman’s python. A patch bump is harmless, but 3.15 takes 3.14 away, and the uv tool docs are blunt about the result: “If the Python version used by a tool is uninstalled, the tool environment will be broken and the tool may be unusable.”

Install a managed interpreter first, then pin the tool to it:

uv python install 3.14
uv tool install --managed-python --reinstall b2

That moves home to ~/.local/share/uv/python/.

The python-preference setting defaults to managed, but uv’s docs add that “system Python installations are still preferred over downloading a managed Python version.” So the tool follows Arch’s upgrade schedule.