| name | cost-burn |
| description | Burn-rate trend over time with optional drift-alert exit code. Bins session spend into buckets, surfaces window-over-window delta, and can exit 1 when latest bucket exceeds prior mean by a configurable %. Distinct from `cost-trend` (benchmark drift); this tracks PRODUCTION spend trajectory. |
| argument-hint | [--bucket 1d] [--lookback 14d] [--alert-on-acceleration-pct 50] [--format table|json] |
| allowed-tools | Bash |
Burn-rate trend observability. The fourth leg of the cost-tracker forward-cost stack:
| Question | Skill |
|---|
| "Have we crossed a threshold?" (reactive) | cost-budget-check |
| "When will we cross a threshold?" (predictive) | cost-projection |
| "Could we have spent less?" (comparative) | cost-counterfactual |
| "Is daily burn ACCELERATING?" (trend) | cost-burn ← this |
Algorithm
Implementation: scripts/burn.mjs.
- Read all
session-* records from cost-tracking namespace.
- Bin into
--bucket duration windows (default 1d) over --lookback (default 14d).
- For each bucket:
{n: sessions, spendUsd: sum(total_cost_usd)}.
- Compute
delta = latest.spendUsd - mean(prior non-empty buckets).
- If
--alert-on-acceleration-pct N is set: exit 1 when deltaPct > N.
Smoke transcript (5 days @ $0.10/day, today $0.50 — 400% acceleration)
| Latest bucket spend | $0.500000 (1 sessions) |
| Prior bucket mean | $0.100000 (4 non-empty buckets) |
| **Delta (latest vs prior mean)** | **+$0.400000 (400.00%)** |
# | Window | Sessions | Spend
0 | 2026-06-15 14:16 → 2026-06-16 14:16 | 1 | $0.500000
1 | 2026-06-14 14:16 → 2026-06-15 14:16 | 0 | $0.000000
2 | 2026-06-13 14:16 → 2026-06-14 14:16 | 1 | $0.100000
3 | 2026-06-12 14:16 → 2026-06-13 14:16 | 1 | $0.100000
...
Drift alert exit code
$ cost burn --bucket 1d --lookback 7d --alert-on-acceleration-pct 50
⚠ ALERT: latest bucket $0.500000 is 400.0% above prior mean $0.100000 (threshold +50%)
exit 1
$ cost burn --bucket 1d --lookback 7d --alert-on-acceleration-pct 500
✓ latest bucket within +500% of prior mean (actual delta: 400.0%) — OK
exit 0
CI integration
cost burn --bucket 1d --lookback 7d --alert-on-acceleration-pct 100 || alert-oncall
The alert is independent of budget — it triggers on rate ACCELERATION even
when total spend is well under budget. Catches "we shipped a hot loop that
burns 10× normal" before the budget alarm goes off.
Distinct from cost-trend
| Skill | Data source | Question |
|---|
cost-trend | docs/benchmarks/runs/*.json | "Is the benchmark drifting (win rate, latency)?" |
cost-burn | cost-tracking namespace | "Is production spend accelerating?" |
Both useful; they answer different questions on different data.
Edge cases
- Sparse history (no prior non-empty buckets): alert is SKIPPED with a reason string, exit 0. Operators don't get spurious alerts on cold-start.
- Prior buckets all $0 but latest > $0: delta is
Infinity/null in JSON, marked new in the table. No alert fires (no baseline to compare against).
--bucket > --lookback: hard error, exit 2.
