@mcp-ui/client

Establishes and manages bidirectional connections to Model Context Protocol servers using WebSocket or stdio transports. Handles authentication handshakes, protocol version negotiation, and connection lifecycle (connect, reconnect, disconnect) with automatic error recovery and heartbeat monitoring to maintain persistent server communication.

Executes remote methods on MCP servers by serializing function calls into JSON-RPC 2.0 messages, correlating responses via message IDs, and deserializing results back into native JavaScript objects. Implements timeout handling, error propagation, and automatic request queuing for concurrent calls to the same server.

Automatically deduplicates identical concurrent requests to the same method with the same parameters, returning cached results instead of sending duplicate RPC calls. Implements time-to-live (TTL) based cache expiration and manual cache invalidation for stale data.

Automatically retries failed RPC calls using exponential backoff with configurable jitter to avoid thundering herd problems. Implements retry budgets and circuit breaker patterns to prevent cascading failures when servers are overloaded or temporarily unavailable.

Queries MCP servers to enumerate available resources, tools, and prompts with their schemas, descriptions, and input/output specifications. Caches metadata locally to avoid repeated server queries and provides type-safe interfaces for accessing resource definitions without manual schema parsing.

Processes streaming responses from MCP servers using event-based handlers that emit data chunks as they arrive, enabling progressive rendering and real-time feedback without buffering entire responses. Implements backpressure handling to prevent memory overflow when server sends data faster than client consumes.

Captures and propagates errors from MCP servers with full context including request ID, method name, and server error details. Distinguishes between transport errors (connection failures), protocol errors (malformed messages), and application errors (RPC failures) to enable targeted error handling strategies.

Provides TypeScript interfaces and runtime validation for RPC method calls, ensuring parameters match server schemas before transmission and validating responses against expected types. Uses JSON Schema validation or similar mechanisms to catch type mismatches early and provide IDE autocomplete for available methods.

Registers event handlers for server-initiated notifications and events, enabling push-based communication patterns where servers notify clients of state changes or important events without polling. Implements subscription management with automatic cleanup and deduplication of event handlers.

Groups multiple RPC calls into a single batch request that executes atomically on the server, either all succeeding or all failing together. Reduces round-trip latency and network overhead compared to sequential calls while maintaining transactional guarantees when supported by the server.

Provides middleware hooks that intercept RPC calls before transmission and responses after receipt, enabling cross-cutting concerns like logging, metrics collection, request transformation, and authentication injection. Implements a chain-of-responsibility pattern where each middleware can modify, skip, or reject requests.

Manages connections to multiple MCP servers simultaneously, reusing connections for multiple concurrent requests and distributing load across available servers. Implements connection pooling with configurable pool size, idle timeout, and automatic cleanup of stale connections.