Claude Code already has /usage (same as /cost). On a Pro or Max plan it will show session cost estimates, plan bars, and a recent breakdown of usage by skill, subagent, plugin, and MCP server.
But, I wanted to optimize Claude, or have it optimize itself, rather than tell me. Skills I installed months ago were sitting idle, and contributing tokens each turn. /usage is good at showing what ran and what counted against the plan. It does not answer: what is installed, still loads, and has not fired once across the last stretch of my own transcripts?
That is what session-tax is for.
What it actually measures
It reads your Claude Code session transcripts off disk on your machine. No network calls in the free script. Imports are fs, path, and os.
