Your monthly Claude Code bill went up 20%. You know that much. What you don't know is which Skill did it — and nothing in the tooling will tell you.
Run /usage in Claude Code and you get claude-sonnet-4-6: ¥3,240 — a per-model total and nothing else. "More expensive than last week" is visible. "Which Skill caused it" is not. usage-breakdown.sh closes that gap. It's a 106-line shell script that parses transcript.jsonl with Python and tallies call counts per Skill, Agent, and MCP server using Counter.
This article walks through how the script works and how to run it, with the actual code and actual numbers.
Why This Approach Works
What Claude Code Is Actually Recording
