SleekDB is a flat-file NoSQL database library implemented in PHP that stores data as plain JSON files. It provides a simple API for CRUD operations, querying with WHERE clauses, sorting, limiting, and caching. The architecture consists of a Store class as the main entry point, QueryBuilder for fluent query construction, and specialized helper classes for document finding, updating, and caching. Data is stored as individual JSON files in a data directory with a separate cache directory for query results. The library requires no third-party dependencies beyond PHP 8.4+ with JSON and MBString extensions. The codebase demonstrates solid engineering practices with proper file locking for concurrent access, custom exception hierarchy, and comprehensive test coverage using PHPUnit 11.0. The query builder follows the builder pattern with method chaining. Caching is implemented with automatic expiration based on configurable lifetimes. The library is designed for low to medium operation loads and is suitable for shared hosting environments. Some deprecated methods are marked for removal in version 3.0, indicating active maintenance and refactoring. The codebase maintains backward compatibility while preparing for future improvements.