A GitHub Actions bill rarely grows because of one decision. It grows a minute at a time: every job is rounded up to a whole minute, every matrix leg pays for its own checkout and setup, macOS minutes cost about ten times as much as Linux minutes, and artifacts stay in storage for 90 days unless you say otherwise. For a mobile team, the most expensive job is often the iOS build. In the pipeline we tested, it was a median 57% of GitHub's cost per run, although the Android build took longer.

We measured both halves of the problem. First, a read-only script that shows where one repository's minutes went in the last 30 days, and the free changes that act on what it finds. Then the runner question.…