performance

# Performance <!-- routing-eval reads this line; it lives in the BODY so the always-on skill LISTING stays inside Claude Code's budget (1% of the context window) — an overflowing listing gets descriptions truncated or dropped, which strips the very keywords a match depends on. --> Trigger phrases: "performance", "slow", "optimization", "profiling", "N+1", "latency", "memory leak", "load test" Core rule: **measure first, optimize later.** Optimization without measurement is a guess; it usually speeds up the wrong place and adds complexity. Stack-agnostic; do a web search when you need the profiling tool/library. ## Method (in order) 1. **Set a target** — what is "acceptable"? (p95 latency, throughput, memory ceiling). Numeric. 2. **Measure** — find the real bottleneck with a profiler/APM/benchmark; don't start from a guess. 3. **Fix the single most expensive thing** — Amdahl: speeding up a 5% path by 2x is wasted; target the hot path. 4. **Measure again** — did it actually improve, is there a regression. 5. **Stop** — once you hit the target, finish; no endless micro-optimization. ## Common bottlenecks Catalog of common bottlenecks + fixes to consult: **`references/bottlenecks.md`**. ## Measurement tips - Measure **under load** (a single request misleads); with a realistic data volume. - **Not p50, but p95/p99** — tail latency is what burns the user. - Don't trust micro-benchmarks; an end-to-end profile is more honest. ## Invariant rules 1. **Don't optimize wi...