Databases Skills

TanStack Query (React Query) best practices for data fetching, caching, mutations, and server state management. Activate when building data-driven React applications with server state.

Use for bun:sqlite, SQLite operations, prepared statements, transactions, and queries.

Cloudflare D1 serverless SQLite on edge. Use for databases, migrations, bindings, or encountering D1_ERROR, statement too long, too many requests queued errors.

Cloudflare Hyperdrive for Workers-to-database connections with pooling and caching. Use for PostgreSQL/MySQL, Drizzle/Prisma, or encountering pool errors, TLS issues, connection refused.

| Type-safe ORM for Cloudflare D1 databases using Drizzle. Use when: building D1 database schemas, writing type-safe SQL queries, managing migrations with Drizzle Kit, defining table relations, implementing prepared statements, using D1 batch API, or encountering D1_ERROR, transaction errors, foreign key constraint failures, or schema inference issues.

Idempotent API operations with idempotency keys, Redis caching, DB constraints. Use for payment systems, webhook retries, safe retries, or encountering duplicate processing, race conditions, key expiry errors.

| Nuxt 4 server-side development with Nitro: API routes, server middleware, database integration, and backend patterns. Use when: creating server API routes, implementing server middleware, integrating databases (D1, PostgreSQL, Drizzle), handling file uploads, implementing WebSockets, or building backend logic with Nitro.

Nuxt 5 server-side development with Nitro v3, h3 v2, API routes, middleware, and database integration. Use when creating server routes, integrating D1/Drizzle, or migrating from Nitro v2.

Implements secure session management with JWT tokens, Redis storage, refresh flows, and proper cookie configuration. Use when building authentication systems, managing user sessions, or implementing secure logout functionality.

TanStack Query v5 (React Query) server state management. Use for data fetching, caching, mutations, or encountering v4 migration, stale data, invalidation errors.

TanStack Table v8 headless data tables with server-side features for Cloudflare Workers + D1. Use for pagination, filtering, sorting, virtualization, or encountering state management, TanStack Query coordination, URL sync errors.

Initialize a project_brain.db in the current project folder. Creates the database, project record, then scans existing files (CLAUDE.local.md, memory files, docs, emails) to bootstrap the brain with knowledge. Smart enough to handle re-runs — skips what already exists and only processes new/changed files.

SQLite-based project knowledge tracker. Manages entities, relationships, tasks, threads, decisions, and events per project folder. Use /brain to query or update project_brain.db. Triggers on: 'brain', 'project knowledge', 'what do we know about', 'open tasks', 'recent decisions'.

Read the recent M0 operational thread for a project, newest first, to pick up work started in this or another tool. Answers 'where were we' and 'what is next' before asking the user to repeat context. Local SQLite, no embeddings, no network. Triggers on: 'm0 recall', 'where were we', 'what did we do last time', 'catch me up', 'resume context', 'read the thread', 'what is next'.

Generate tests for database migration safety covering schema changes, data integrity preservation, rollback verification, and zero-downtime migration validation

Database performance testing including query optimization, index analysis, connection pooling, slow query detection, and N+1 query prevention.

Testing database migration scripts for correctness, rollback safety, data integrity, and zero-downtime migration patterns.

Testing patterns for Drizzle ORM covering migration testing, query builder testing, transaction testing, and database integration testing with PostgreSQL, SQLite, and MySQL.

MongoDB testing with in-memory MongoDB, aggregation pipeline testing, schema validation, indexing verification, and replica set testing.

Detect and eliminate N+1 query problems in database-backed applications through query counting, execution plan analysis, and ORM configuration auditing

Redis testing including cache behavior verification, pub/sub testing, transaction testing, cluster failover testing, and data expiration validation.

Testing patterns for Supabase applications covering auth flow testing, Row Level Security policy testing, realtime subscription testing, and edge function testing

Test isolation techniques including database cleanup, transaction rollback, parallel test execution, and shared resource management.

Teaches the agent to speed up Node integration tests with Testcontainers reuse — withReuse(true), TESTCONTAINERS_REUSE_ENABLE, the .testcontainers.properties opt-in, stable hashing for Postgres/MySQL/Kafka, and Ryuk/CI caveats.

> Use when creating database migrations, schema changes, seed data, or any SQL that modifies database structure. Covers Flyway naming conventions, versioning, and safe migration patterns.

> Use when implementing caching, session storage, rate limiting, or any Redis integration. Covers cache-aside pattern, key naming, TTL strategy, and serialization config.

> Use when working with @Transactional, multi-step database operations, distributed transactions, or any code that needs atomicity guarantees. Covers propagation rules, isolation levels, read-only optimization, and common pitfalls.

> Use when creating database migrations, schema changes, seed data, or any SQL that modifies database structure. Covers Flyway naming conventions, versioning, and safe migration patterns.

> Use when implementing caching, session storage, rate limiting, or any Redis integration. Covers cache-aside pattern, key naming, TTL strategy, and serialization config.

> Use when working with @Transactional, multi-step database operations, distributed transactions, or any code that needs atomicity guarantees. Covers propagation rules, isolation levels, read-only optimization, and common pitfalls.

Expert in background job processing with Bull/BullMQ (Redis), Celery, and cloud queues. Implements retries, scheduling, priority queues, and worker management. Use for async task processing, email campaigns, report generation, batch operations. Activate on "background job", "async task", "queue", "worker", "BullMQ", "Celery". NOT for real-time WebSocket communication, synchronous API calls, or simple setTimeout operations.

Design multi-tier caching architectures for web applications — cache-aside vs write-through vs write-behind, TTL design, cache invalidation, Redis patterns, CDN configuration, browser caching, and stampede prevention. Use when choosing a caching pattern, designing cache invalidation strategies, implementing Redis caching, configuring Cache-Control headers, or preventing cache stampedes. Activate on "cache invalidation", "cache-aside", "write-through", "TTL", "Redis cache", "CDN caching", "cache stampede", "stale data", "browser cache". NOT for database query caching within an ORM, memoization of pure functions, or CPU-level caching.

Application architecture patterns and code organization — clean architecture, hexagonal architecture, feature-based structure, dependency inversion, module boundaries, SOLID principles at module scale. Activate on "clean architecture", "hexagonal architecture", "feature-based structure", "dependency inversion", "module boundaries", "architecture pattern", "folder structure", "fat controller", "circular dependency", "IoC container". NOT for microservice decomposition (use microservices-patterns) or database schema design (use database-design-patterns).

Schema design, normalization decisions, indexing strategies, and migration safety for relational databases. Use when designing tables, choosing between normalize vs denormalize, selecting index types, planning zero-downtime migrations, or setting up connection pooling. Activate on "schema design", "normalization", "denormalization", "foreign key", "index strategy", "migration", "connection pooling", "composite key", "surrogate key", "soft delete", "polymorphic association". NOT for PostgreSQL-specific query tuning or EXPLAIN analysis (use postgresql-optimization), NoSQL or document database design, or cloud database provisioning.

Drizzle ORM schema management and SQLite migrations — adding tables, modifying columns, creating indexes, generating and running migrations, Drizzle query patterns. NOT for Prisma, TypeORM, Sequelize, or raw SQL migration tools.

Application performance profiling and bottleneck identification — Node.js profiling, Chrome DevTools, flame graphs, memory leak detection, CPU profiling, React rendering performance. Activate on "profiling", "performance bottleneck", "flame graph", "memory leak", "slow app", "CPU profiling", "heap snapshot", "React re-renders", "EXPLAIN ANALYZE", "event loop lag", "clinic.js", "Core Web Vitals". NOT for infrastructure monitoring or observability (use logging-observability), load testing (use a load-testing skill), or database schema optimization.

Expert in PostgreSQL performance tuning, query optimization, and database administration. Specializes in EXPLAIN analysis, indexing strategies, connection pooling, partitioning, and production-grade PostgreSQL operations.

Prepare for L6+ coding interviews — in-memory databases, concurrency, state management, iterative follow-ups. Use when practicing real-world system-building problems or preparing communication strategies for live coding. Activate on "coding interview", "staff interview", "codesignal", "live coding", "rate limiter interview". NOT for LeetCode/competitive programming, behavioral interviews, or system design whiteboard.

Supabase administration, RLS policies, migrations, and schema design. Use for database architecture, Row Level Security, performance tuning, auth integration. Activate on "Supabase", "RLS", "migration", "policy", "schema", "auth.uid()". NOT for Supabase Auth UI configuration (use dashboard), edge functions (use cloudflare-worker-dev), or general SQL without Supabase context.

Design and manage reference data systems — security master, client master, account master, identifier mapping, pricing data sources, golden source designation, and governance. Use when building or evaluating a security master database, mapping identifiers across systems (CUSIP to ISIN, SEDOL to FIGI), designing client master models for onboarding or KYC, defining account master attributes across custodians, designating golden sources and MDM patterns across systems, establishing a pricing vendor hierarchy with fallback order, establishing reference data governance and stewardship, handling identifier changes from corporate actions, or troubleshooting issues traced to missing or changed identifiers. Trigger on: security master, CUSIP, ISIN, SEDOL, FIGI, client master, account master, pricing data, reference data, golden source, MDM, master data, identifier mapping, data governance, vendor hierarchy.

> Use when performing database operations in ERPNext/Frappe v14-v16. Covers frappe.db methods, ORM patterns (frappe.get_doc, frappe.get_list), raw SQL, caching patterns, and performance optimization. Prevents common mistakes frappe.get_doc, database query, SQL, ORM, caching, database performance, query returns nothing, slow database, how to fetch data, get document by name, frappe.get_list empty.

> Use when implementing Redis caching, cache invalidation, or distributed locking in Frappe. Prevents stale cache bugs, race conditions from missing locks, and memory bloat from unbounded cache keys. Covers frappe.cache(), @redis_cache decorator, cache.get_value/set_value, cache invalidation patterns, frappe.lock, TTL strategies.

> Use when handling database errors in Frappe/ERPNext. Covers DuplicateEntryError, LinkValidationError, MandatoryError, TimestampMismatchError, CharacterLengthExceededError, InReadOnlyMode, QueryTimeoutError, SQL injection errors, frappe.db.sql parameter format (% vs %s), get_value returning None, transaction deadlocks, MariaDB gone away, too many connections. Error-to-fix mapping for v14/v15/v16. SQL injection, deadlock, MariaDB gone away, query timeout.

> Use when tuning MariaDB, configuring Redis memory, sizing Gunicorn workers, setting up CDN, or profiling slow queries. Prevents performance bottlenecks from default configurations, memory exhaustion, and unoptimized database queries. Covers MariaDB tuning, Redis configuration, Gunicorn worker sizing, CDN setup, slow query log analysis, Python profiling, request profiling.

> Use when building database queries with frappe.qb in Frappe v14-v16. joins, aggregation, subqueries, cross-DB compatibility (MariaDB/PostgreSQL), and migration from raw SQL. Prevents SQL injection and DB-specific bugs. aggregate, ImportMapper, cross-database, parameterized query.

> (1) Finding similar structures in PDB/AFDB databases, (2) Structural homology search, (3) Database queries by 3D structure, (4) Finding remote homologs not detected by sequence, (5) Clustering structures by similarity. For sequence similarity, use uniprot BLAST. For structure prediction, use chai or boltz.

> Use when the user wants to iteratively improve an artifact under a hard correctness bound while minimizing a measured cost — refactoring a code module to cut complexity while its test suite stays green, OR speeding up a SQL query while it returns the same rows. Each iteration applies one focused change, checks a correctness gate that must pass, measures a metric that must drop, and keeps the change only if both hold, else reverts; loops to a plateau or budget. Not for adding features, fixing bugs, or any change that is allowed to alter behaviour or results.

Create, schedule, and verify database backups with support for full, incremental, and point-in-time recovery strategies.