Claude Code exposes `rate_limits` to exactly one place, and statusLine is the hook that reaches it.

claude-usage-monitor documents something useful independent of the tool: Claude Code delivers a rate_limits object as JSON on stdin to the statusLine command and nowhere else. No tool, no environment variable, no CLI command exposes remaining usage to a running agent. The project uses that channel to inject a one-per-window warning naming percentage used and minutes to reset, so a long refactor writes down its state before a force-stop. Running unattended agents means statusLine is your only read on that number.