SpiceDB is an open-source implementation of Google's Zanzibar paper, which provides a comprehensive relationship-based access control system. The project translates the major concepts of the Zanzibar paper into its own architecture and design, offering a robust and scalable solution for managing permissions in distributed systems. SpiceDB uses gRPC as its primary interface for receiving requests, with additional support for HTTP/2 or binary payloads when necessary. It employs a validation process that includes protobuf, semantic validation, and data-driven semantic validation to ensure the integrity of incoming requests. The system handles various types of operations, including CRUD operations on relationships, schema, and permissions, using a dispatch interface that breaks down complex requests into smaller, cacheable sub-problems. SpiceDB also features caching, remote dispatch, and proxy implementations for the datastore interface, which provides a flexible and scalable storage layer for relationship and schema data. The project aims to provide a powerful solution for managing permissions in distributed systems, with a strong focus on scalability, reliability, and performance.