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+---
+name: ck:databases
+description: Design schemas, write queries for MongoDB and PostgreSQL. Use for database design, SQL/NoSQL queries, aggregation pipelines, indexes, migrations, replication, performance optimization, psql CLI.
+license: MIT
+argument-hint: "[query or schema task]"
+metadata:
+  author: claudekit
+  version: "1.0.0"
+---
+
+# Databases Skill
+
+Unified guide for working with MongoDB (document-oriented) and PostgreSQL (relational) databases. Choose the right database for your use case and master both systems.
+
+## When to Use This Skill
+
+Use when:
+- Designing database schemas and data models
+- Writing queries (SQL or MongoDB query language)
+- Building aggregation pipelines or complex joins
+- Optimizing indexes and query performance
+- Implementing database migrations
+- Setting up replication, sharding, or clustering
+- Configuring backups and disaster recovery
+- Managing database users and permissions
+- Analyzing slow queries and performance issues
+- Administering production database deployments
+
+## Reference Navigation
+
+### Database Design
+- **[db-design.md](references/db-design.md)** - Activate when user requests: Database/table design for transactional (OLTP), analytics (OLAP), create or extend schema, design fact/dimension tables, analyze/review CSV/JSON/SQL files to create tables, or need advice on data storage structure.
+
+### MongoDB References
+- **[mongodb-crud.md](references/mongodb-crud.md)** - CRUD operations, query operators, atomic updates
+- **[mongodb-aggregation.md](references/mongodb-aggregation.md)** - Aggregation pipeline, stages, operators, patterns
+- **[mongodb-indexing.md](references/mongodb-indexing.md)** - Index types, compound indexes, performance optimization
+- **[mongodb-atlas.md](references/mongodb-atlas.md)** - Atlas cloud setup, clusters, monitoring, search
+
+### PostgreSQL References
+- **[postgresql-queries.md](references/postgresql-queries.md)** - SELECT, JOINs, subqueries, CTEs, window functions
+- **[postgresql-psql-cli.md](references/postgresql-psql-cli.md)** - psql commands, meta-commands, scripting
+- **[postgresql-performance.md](references/postgresql-performance.md)** - EXPLAIN, query optimization, vacuum, indexes
+- **[postgresql-administration.md](references/postgresql-administration.md)** - User management, backups, replication, maintenance
+
+## Python Utilities
+
+Database utility scripts in `scripts/`:
+- **db_migrate.py** - Generate and apply migrations for both databases (MongoDB and PostgreSQL)
+- **db_backup.py** - Backup and restore MongoDB and PostgreSQL
+- **db_performance_check.py** - Analyze slow queries and recommend indexes
+
+```bash
+# Generate migration
+python scripts/db_migrate.py --db mongodb --generate "add_user_index"
+
+# Run backup
+python scripts/db_backup.py --db postgres --output /backups/
+
+# Check performance
+python scripts/db_performance_check.py --db mongodb --threshold 100ms
+```
+
+## Best Practices
+
+**MongoDB:**
+- Use embedded documents for 1-to-few relationships
+- Reference documents for 1-to-many or many-to-many
+- Index frequently queried fields
+- Use aggregation pipeline for complex transformations
+- Enable authentication and TLS in production
+- Use Atlas for managed hosting
+
+**PostgreSQL:**
+- Normalize schema to 3NF, denormalize for performance
+- Use foreign keys for referential integrity
+- Index foreign keys and frequently filtered columns
+- Use EXPLAIN ANALYZE to optimize queries
+- Regular VACUUM and ANALYZE maintenance
+- Connection pooling (pgBouncer) for web apps
+
+## Resources
+
+- MongoDB: https://www.mongodb.com/docs/
+- PostgreSQL: https://www.postgresql.org/docs/
+- MongoDB University: https://learn.mongodb.com/
+- PostgreSQL Tutorial: https://www.postgresqltutorial.com/