Guides clean, scalable system architecture during the build phase. Use when designing modules, defining boundaries, structuring projects, managing dependencies, or preventing tight coupling and brittleness as systems grow.

Fixes flaky tests by replacing arbitrary timeouts with condition polling. Use when tests fail intermittently, have setTimeout delays, or involve async operations that need proper wait conditions.

Best practices for writing Claude Code skills, rules, and CLAUDE.md instructions. Use when creating SKILL.md files, authoring .claude/rules, writing CLAUDE.md project or user instructions, or configuring Claude behavior for a project or team.

Diagnose and fix tests that pass in isolation but fail when run concurrently. Covers shared state isolation and resource conflicts. References condition-based-waiting for timing issues.

Prevents silent failures and context loss in error handling. Use when writing try-catch blocks, designing error propagation, reviewing catch blocks, or implementing Result patterns.

Guides database architecture decisions for PostgreSQL, DuckDB, Parquet, PGVector, and Neo4j. Use when designing schemas, choosing storage strategies, optimizing queries, tuning maintenance, configuring vector search, modeling graph data, or diagnosing performance issues across OLTP, OLAP, similarity search, and graph workloads.

Safe code migrations with backward compatibility and reversibility. Use when upgrading dependencies, changing database schemas, API versioning, or transitioning between technologies.

Defines product features from a PM perspective before technical planning begins. Use when scoping new features, writing product specs, defining user problems, choosing what to build, researching existing patterns, or bridging the gap between strategy and implementation. Covers JTBD analysis, competitive research, UX/DX experience definition, and scope negotiation for consumer, B2B, and developer tool products.

Review a completed session to extract actionable improvements. Identifies DX friction, documentation gaps, architectural confusion, anti-patterns, process failures, and skill/config improvements. Uses progressive disclosure for targeted investigation types.

Detect and run project linters, formatters, and type checkers before committing or claiming completion. Auto-detects tools from project config files.

Analyzes logs efficiently through targeted search and iterative refinement. Use when investigating errors, debugging incidents, or analyzing patterns in application logs.

Improves code structure while preserving behavior through test verification. Use when cleaning up code, reducing duplication, simplifying complexity, or reorganizing modules.

Produces executive-quality strategic documents in The Economist/HBR style. Use when writing strategy memos, market analysis, business cases, customer research reports, or any document for Product, Design, and Business leaders. Customer-led, evidence-based, narrative-driven.

Creates professional Mermaid diagrams with semantic styling and visual hierarchy. Use when creating flowcharts, sequence diagrams, state machines, class diagrams, or architecture visualizations.

Writes behavior-focused tests using Testing Trophy model with real dependencies. Use when writing tests, choosing test types, or avoiding anti-patterns like testing mocks.