Performance Profiler

Systematic performance profiling for Node.js, Python, and Go applications. Identifies CPU bottlenecks with flamegraphs, detects memory leaks with heap snapshots, analyzes bundle sizes, optimizes database queries, detects N+1 patterns, and runs load tests with k6 and Artillery. Enforces a measure-first methodology: establish baseline, identify bottleneck, fix, and verify improvement.

Golden Rule — Measure First: Profile → Confirm bottleneck → Fix → Measure again → Verify improvement. Every optimization needs baseline metrics, profiler evidence, the fix, post-fix metrics, and a delta. Full rule in references/cpu-and-memory-profiling.md.

Core Capabilities

• CPU profiling — Clinic.js/V8 flamegraphs (Node), py-spy/cProfile/scalene (Python), pprof (Go), Chrome DevTools (browser).
• Memory profiling — heap snapshots and before/after comparison, GC pressure analysis, leak detection, retained object graphs.
• Database optimization — EXPLAIN ANALYZE plan reading, N+1 detection and batching, slow query logs, missing-index identification, connection pool sizing.
• Bundle analysis — webpack/Next.js analyzers, tree-shaking, dynamic imports, heavy dependency identification.
• Load testing — k6 ramp-up scripts, SLA threshold enforcement in CI, P50/P95/P99 latency tracking, concurrent user simulation.

When to Use

• App is slow and you do not know where the bottleneck is.
• P99 latency exceeds SLA before a release.
• Memory usage grows over time (suspected leak).
• Bundle size increased after adding dependencies.
• Preparing for a traffic spike (load test before launch).
• Database queries taking >100ms, or verifying no regressions after a dependency upgrade.

Clarify First

Before profiling, confirm these inputs. If any is unknown or vague, ASK — do not assume:

• Runtime & symptom — Node / Python / Go and CPU / memory / bundle / query / load-spike (selects the profiler and toolchain)
• Baseline + SLA target — current numbers and the P95/P99 (or size) threshold to beat (measure-first needs both to verify a delta)
• Environment — local / staging / prod determines the safe profiling method and whether load testing is allowed

Stop rule: ask only the 2-3 that most change the output. If the user says "just draft it," proceed and list your assumptions at the top of the artifact.

Tools

All three accept a file path or - for stdin and support --json.

References

Load the reference that matches the task — keep this file lean and pull detail on demand:

• references/cpu-and-memory-profiling.md — the full Measure-First rule, Node.js CPU profiling (Clinic.js flamegraphs, V8 CPU profiles), and memory leak detection (Node heap snapshots, Python memray/tracemalloc). Read when chasing CPU or memory issues.
• references/database-and-bundle.md — EXPLAIN ANALYZE workflow, N+1 detection patterns and middleware script, Next.js bundle analyzer setup, quick size checks, and the common-bundle-wins table. Read when optimizing queries or bundle size.
• references/load-testing-and-methodology.md — full k6 load-test script, the before/after measurement template, quick-win optimization checklist, common pitfalls, best practices, troubleshooting table, and success criteria. Read when load testing or documenting a win.

Scope & Limitations

This skill covers:

• CPU and memory profiling for Node.js, Python, and Go applications using flamegraphs and heap snapshots
• Database query optimization including EXPLAIN ANALYZE interpretation, N+1 detection, and index recommendations
• Frontend bundle analysis and size reduction strategies for webpack and Next.js projects
• Load testing methodology with k6 including ramp-up patterns, threshold enforcement, and CI integration

This skill does NOT cover:

• Application Performance Monitoring (APM) platform setup and configuration (Datadog, New Relic, Grafana) — see engineering/observability-designer
• Infrastructure-level performance tuning (kernel parameters, network stack, container resource limits) — see engineering/senior-devops
• Security-focused performance concerns such as DDoS mitigation or rate limiting — see engineering/senior-security
• Mobile application profiling (iOS Instruments, Android Profiler) — see engineering/senior-mobile

Integration Points