Setup Cost Tracking

Installs genuine cost capture for every Claude Code session on this machine. Cost data (cost.total_cost_usd etc.) is computed by Claude Code itself and is available only in the statusline payload — hooks never receive it. So this skill wires a logger into the statusline path while preserving whatever statusline and hooks the user already has.

What gets installed

Bundled in this skill's scripts/ directory, copied to ~/.claude/scripts/:

Script	Role
cost-logger.js	Capture engine. Silent, crash-proof. Writes the log files below.
statusline-wrapper.js	Used when the user already has a statusline: logs cost, then delegates the payload to their original command and passes its output through untouched.
statusline-command.js	Used when the user has no statusline: full display (model, context bar, cost, cache stats) that also logs.
turn-logger.js	Stop hook: stamps turn boundaries so cost samples can later be grouped into turns for analytics. No cost data itself.

Log outputs (created lazily, no setup needed):

• ~/.claude/cost-log.jsonl — one row per session, exact cumulative totals (upserted).
• ~/.claude/projects/<mapped-dir>/<session>.cost.jsonl — cost samples at ~5s resolution during activity.
• ~/.claude/projects/<mapped-dir>/<session>.turn-boundaries.jsonl — one row per turn end, with transcript_path for deep-dive analytics.

Installation procedure

Follow these steps exactly. Use real JSON manipulation (a node -e script or jq) for every settings edit — never string/regex edits on settings files.

Step 0 — Preflight

1. command -v node — if Node.js is missing, stop and tell the user it's required. Record the absolute path (call it $NODE). Use $NODE in every command you write into settings, not bare node (statusline/hook commands don't always get the user's full shell PATH).
2. Read ~/.claude/settings.json (treat as {} if absent) and ~/.claude/settings.local.json (if present). The effective statusLine is the local one if defined there, else the user one. Remember which file defines it — edits must go to that same file.

Step 1 — Copy scripts

1. mkdir -p ~/.claude/scripts
2. Copy the four .js files from this skill's scripts/ directory into ~/.claude/scripts/ and chmod +x them. Overwriting previous versions of these four files is fine (that's how upgrades work). Never overwrite ~/.claude/scripts/statusline-original.json if it exists.

Step 2 — Wire the statusline (the load-bearing step)

Decide by the effective statusLine:

• Case A — already ours: its command contains statusline-wrapper.js or statusline-command.js. Nothing to change; report "already installed" and continue to Step 3.
• Case B — none configured: set in ~/.claude/settings.json:

  "statusLine": { "type": "command", "command": "$NODE /Users/<user>/.claude/scripts/statusline-command.js", "padding": 0 }
  

  (expand $NODE and the home directory to absolute paths).
• Case C — user has their own statusline: preserve it.
  1. Write ~/.claude/scripts/statusline-original.json containing exactly { "command": "<their current statusLine.command>" }.
  2. In the file that defines statusLine, replace only the command value with $NODE /Users/<user>/.claude/scripts/statusline-wrapper.js. Keep type, padding, refreshInterval, and any other sibling keys untouched.

Before the first edit to any settings file, back it up: cp settings.json settings.json.bak-cost-tracking (same pattern for the local file). One backup per run is enough.

Step 3 — Add the turn-boundary hook (additive, never replaces)

If no existing hooks.Stop entry's command mentions turn-logger.js, append this entry to the hooks.Stop array (create the array/path if missing), leaving every existing hook alone:

{ "matcher": "", "hooks": [ { "type": "command", "command": "$NODE /Users/<user>/.claude/scripts/turn-logger.js" } ] }

This hook carries no cost data — it only stamps turn boundaries and the idle timer. If the user objects to hooks, skipping this step still leaves session cost capture fully working.

Step 4 — Verify

1. Build a fake statusline payload with session_id "cost-setup-verify", a workspace.current_dir of /tmp/cost-setup-verify, and nonzero cost.total_cost_usd / cost.total_api_duration_ms / model.display_name values.
2. Pipe it via stdin into the exact statusLine.command now in settings (run through sh -c).
   • Case B: expect the rendered multi-line statusline.
   • Case C: expect the original statusline's output (the wrapper delegates). If their original command errors on the synthetic payload, that's their script's quirk — check instead that the log file below was written.
3. Confirm ~/.claude/projects/-tmp-cost-setup-verify/cost-setup-verify.cost.jsonl now exists and contains the fake cost.
4. Clean up all verification artifacts: that projects subdirectory, the cost-setup-verify line in ~/.claude/cost-log.jsonl, and /tmp/statusline-*-cost-setup-verify state files.

Step 5 — Report

Tell the user, concretely:

• which case applied (fresh install / wrapped their existing statusline / already installed),
• every file created or modified (settings edits, backups, copied scripts),
• where their cost data will accumulate (the three log paths above),
• that changes take effect in new sessions,
• how to uninstall: restore the .bak-cost-tracking settings backup (or, by hand: point statusLine.command back to the command saved in ~/.claude/scripts/statusline-original.json and remove the turn-logger Stop hook entry), then delete the four scripts.

Invariants

• Never delete or rewrite the user's hooks, statusline command, or unrelated settings keys. All changes are additive or a single-value swap that is recorded for reversal.
• Idempotent: re-running on an installed machine must change nothing and say so.
• If any step fails midway, restore the settings backup and report what happened.