slo-check — Claude Code skill for SLO checks

---
name: slo-check
description: >
  Define and check simple service-level objectives for Claude Code from Agent
  Monitor data — session completion rate, tool success rate
  (PostToolUse/PreToolUse), and error rate (APIError/total) — then compare each
  to its target and report the error budget remaining. Use when reporting
  reliability or when someone asks "are we meeting our SLOs?".
---

# SLO Check

Turn raw event counts into a clear SLO scorecard with error-budget accounting.

## Input

The user provides: **$ARGUMENTS**

This may be:
- empty — use the default SLO targets below over all available data
- targets like "completion=95 success=99 error=1" — override the defaults (percentages)
- a window like "last 7d" or "today" — restrict the measurement period

Default SLO targets: completion rate ≥ 95%, tool success rate ≥ 99%, error rate ≤ 1%.

## Data Sources

| Endpoint | Returns |
|----------|---------|
| `GET /api/analytics` | `event_types` (PreToolUse, PostToolUse, APIError counts), `sessions_by_status`, `daily_events` (365d), `daily_sessions` (365d) — the raw numerators/denominators for every SLI |
| `GET /api/stats` | `total_sessions`, `total_events`, `events_today`, `sessions_by_status` — fleet totals and recency |
| `GET /api/events?session_id=X` | Per-session stream — drill into the sessions that breach an SLO |

## Report Sections

### 1. Service Level Indicators (SLIs)
Compute each SLI from `GET /api/analytics` / `GET /api/stats`:
- **Completion rate** = completed sessions / total sessions (from `sessions_by_status`; count `active`/`running` as in-flight, exclude them from the denominator if still open).
- **Tool success rate** = `PostToolUse / PreToolUse` (capped at 100%).
- **Error rate** = `APIError / total_events`.
Within a window, derive the numerators/denominators from `daily_events` / `daily_sessions`.

### 2. SLO Scorecard
For each SLI, compare to its target and mark MET ✅ or BREACHED ❌.

### 3. Error Budget
For each objective, report the **error budget** and how much remains:
- Budget = `1 − target` (e.g., 1% for a 99% target).
- For "higher-is-better" SLOs (completion, success): remaining = `(observed − target) / (1 − target)`.
- For "lower-is-better" SLOs (error rate): remaining = `(target − observed) / target`.
- A negative result means the budget is exhausted — report how far over (e.g., "2.7× over budget").

### 4. Breach Drill-Down
For any breached SLO, list the sessions contributing most to the breach (most failed tools or most APIErrors) via `GET /api/events?session_id=X`.

## Output

- A Markdown scorecard table: SLI | observed | target | status | error budget remaining.
- Rates as percentages to 2 decimals; any currency in USD to 4 decimals.
- Cite exact counts and `session_id` values — never fabricate numerators or denominators.
- End with the SLO most at risk and the single action that would recover the most budget.
- Read-only: only report what the API returns. If `curl` cannot reach `http://localhost:4820`, tell the user to start the dashboard with `npm start` from the repo root.