The SDK follows a layered architecture with clear separation of concerns:

• Client/Server Layer (McpClient/McpServer): Both use McpSession for sync/async operations, with McpClient handling client-side protocol operations and McpServer managing server-side protocol operations.
• Session Layer (McpSession): Manages communication patterns and state.
• Transport Layer (McpTransport): Handles JSON-RPC message serialization/deserialization via:
  • StdioTransport (stdin/stdout) in the core module
  • HTTP SSE transports in dedicated transport modules (Java HttpClient, Servlet)
  • Streamable HTTP transports for efficient bidirectional communication
  • Spring WebFlux and Spring WebMVC transports (available in Spring AI 2.0+)

The MCP Client is a key component in the Model Context Protocol (MCP) architecture, responsible for establishing and managing connections with MCP servers. It implements the client-side of the protocol.

The MCP Server is a foundational component in the Model Context Protocol (MCP) architecture that provides tools, resources, and capabilities to clients. It implements the server-side of the protocol.

Key Interactions:

• Client/Server Initialization: Transport setup, protocol compatibility check, capability negotiation, and implementation details exchange.
• Message Flow: JSON-RPC message handling with validation, type-safe response processing, and error handling.
• Resource Management: Resource discovery, URI template-based access, subscription system, and content retrieval.

The SDK is organized into modules to separate concerns and allow adopters to bring in only what they need:

!!! tip A minimal adopter may depend only on mcp (core + Jackson 3). Spring-based applications should use the mcp-spring-webflux or mcp-spring-webmvc artifacts from Spring AI 2.0+ (group org.springframework.ai), no longer part of this SDK.