Summary

When UV_NO_CACHE=1, uv's cache is silently disabled. Running e.g. uv sync --verbose prints helpful messages about other caching behaviour:

2025-09-12T22:56:35.6973502Z DEBUG Searching for a compatible version of setuptools (>=61.0.0)
2025-09-12T22:56:35.6974771Z DEBUG Selecting: setuptools==80.9.0 [compatible] (setuptools-80.9.0-py3-none-any.whl)
2025-09-12T22:56:35.6976727Z DEBUG No cache entry for: https://files.pythonhosted.org/packages/a3/dc/17031897dae0efacfea57dfd3a82fdd2a2aeb58e0ff71b77b87e44edc772/setuptools-80.9.0-py3-none-any.whl.metadata

At no point, however, is the fact that caching is disabled (via UV_NO_CACHE=1) explicitly logged. Adding this logging would be extremely helpful, to me at least.

Ideally, running with UV_NO_CACHE=1 would result in something like:

DEBUG uv's cache has been disabled by UV_NO_CACHE=1. No files will be stored or restored.

Example

I was using vast.ai to run a self-hosted CI runner, using the setup-uv github action.

uv's caching was misbehaving, and I did not understand why. It was only with much digging that I found UV_NO_CACHE=1 had been set by default by Vast's dockerfile.

Thanks for building an incredible tool!