Drift detection for Claude Code, packaged as two installable Agent Skills. Reads the JSONL session logs Claude Code already writes to ~/.claude/projects/, detects whether the model has been drifting on your own work, and produces a shareable forensic report.

No network, no account, no telemetry, no background daemon. Runs on the data already on your disk.

Status: 0.x / pre-alpha — output format and metric set may change.

What you get

Window defaults to 60d. Accepts 7d / 14d / 30d / 60d / 90d / 180d.

Each report includes:

• Verdict — HOLDING / SUSPECTED REGRESSION / CONFIRMED REGRESSION / INCONCLUSIVE
• Headline metrics table (pre vs post, with 🟢/🟡/🔴 band verdicts)
• Weekly trend bars — cost (USD, verified against ccusage to the cent), read:edit ratio, reasoning loops, tokens/turn
• Cross-version comparison — same user, different model versions, controlling for task mix
• Auto-detected inflection date — composite health-score break
• Findings with model-side / user-side / ambiguous classification
• Appendices — hour-of-day thinking depth, word-frequency shift, three-period thinking-visibility transition, per-turn behavior rates, and more

Install

npx skills add delta-hq/cc-canary

Install just one:

npx skills add delta-hq/cc-canary --skill cc-canary
npx skills add delta-hq/cc-canary --skill cc-canary-html

Then from any Claude Code session:

/cc-canary 60d
/cc-canary-html 30d

Requirements: python3 ≥ 3.8 on your PATH. macOS / Linux / WSL for the cc-canary-html auto-open step (it falls back to printing the path if open / xdg-open / start fails).

How it works

1. Scan. A bundled Python script (stdlib only — no pip, no Node) walks ~/.claude/projects/**/*.jsonl, filters by window and excludes subagent sessions by default.
2. Dedupe. Assistant messages are deduped on (message.id, requestId) — same scheme ccusage uses, because Claude Code writes the same message into multiple JSONLs when sessions are resumed or branched.
3. Aggregate. Per-session metrics: tool-mix, read:edit ratio, reasoning-loop phrases, self-admitted errors, premature stops, interrupts, token usage, cost (current Claude 4.x rates), hour-of-day thinking depth.
4. Detect inflection. Composite health score per day; argmax of |before − after| over candidate dates with a 0.75σ floor. Falls back to median-timestamp split if no break clears.
5. Pre-render the report. Script writes a markdown / HTML skeleton with every table and bar chart filled in. Only ~20 short narrative slots (marked <!-- C: ... -->) are left for Claude to fill — verdict line, summary, per-finding reasoning, root-cause, appendix paragraphs.
6. Fill & save. Claude reads the skeleton, writes the narrative, saves the final file.

Total runtime: ~2.5s for the script + 10–20s for Claude to fill narrative.

What each skill tracks

Metrics in the headline table (with published healthy/transition/concerning bands where applicable):

• Read:Edit ratio — file reads per edit. Proxy for how thoroughly the model investigates before mutating.
• Write share of mutations — Write / (Edit + Write). High share = model rewriting files instead of surgical edits.
• Reasoning loops / 1K tool calls — phrases like "let me try again", "oh wait", "actually,".
• Frustration rate — rate of frustration words in your prompts.
• Thinking redaction rate — fraction of thinking blocks that are redacted vs visible.
• Mean thinking length — reasoning-depth proxy (via cryptographic signature length, r=0.97 with content length when visible).
• API turns per user turn — how many API calls the model makes per user message.
• Tokens per user turn — total token volume (input + output + cache) per user message.

Plus appendices with additional signals: premature stopping, self-admitted errors, shortcut vocabulary, user interrupts, hour-of-day thinking depth, per-word frequency shift, three-period thinking-visibility transition, per-turn behavior rates.

Skill filters & flags

The script accepts flags you can pass via Bash(python3 scripts/compute_stats.py …) for custom runs:

Privacy

• Fully local. Zero network calls.
• The script reads ~/.claude/projects/*.jsonl only. Nothing else.
• Narrative prose is written by Claude during the skill invocation (inside your Claude Code session); it has access only to the on-disk files you explicitly point it at.
• User-prompt content is truncated to ≤180 chars before being included in the skeleton, and redacted for /Users/… paths, emails, hex-like tokens.
• Output files (./cc-canary-<date>.{md,html}) live in the directory where you invoked the skill. Nothing is uploaded anywhere.

Contributing

Issues, metric suggestions, and PRs welcome: github.com/delta-hq/cc-canary/issues. Output format and metric set may change during 0.x.

About the name

Canaries were used in coal mines to detect early signs of danger. cc-canary does the same for drift in your Claude Code sessions.

License

MIT