@modelcontextprotocol/server

Implements the Model Context Protocol server-side specification, handling bidirectional JSON-RPC 2.0 message routing between client and server over stdio, HTTP, or SSE transports. Uses an event-driven architecture with request/response correlation and automatic error handling for malformed messages, enabling LLM clients to discover and invoke server-exposed tools and resources.

Provides a declarative API for registering tools with JSON Schema definitions, parameter validation, and execution handlers. Tools are automatically advertised to clients via the list_tools capability, and incoming call_tool requests are routed to registered handlers with automatic parameter extraction and type coercion, supporting both synchronous and asynchronous handler functions.

Enables servers to advertise static or dynamic resources (files, documents, data) with URI schemes and metadata, allowing clients to discover available resources via list_resources and read them via read_resource calls. Supports streaming large resources and custom URI schemes, with automatic metadata caching and client-side filtering based on resource type and annotations.

Allows servers to register reusable prompt templates with named arguments and descriptions, which clients can discover via list_prompts and execute via get_prompt with argument substitution. Templates support dynamic content injection and are useful for standardizing multi-turn conversations or complex reasoning patterns across multiple LLM clients.

Provides pluggable transport implementations for stdio (child process), HTTP (request/response), and Server-Sent Events (SSE) streaming, abstracting away protocol-level message framing and connection management. Each transport handles serialization, error propagation, and connection lifecycle independently, allowing servers to support multiple simultaneous client connections without transport-specific code.

Implements the MCP initialization handshake where servers advertise supported capabilities (tools, resources, prompts) and protocol version, and clients declare their requirements. The server validates compatibility and rejects connections with incompatible protocol versions, ensuring both parties understand the feature set before exchanging data.

Automatically formats all server responses as JSON-RPC 2.0 compliant objects with proper error codes, messages, and data fields. Catches handler exceptions and converts them to structured error responses, ensuring clients receive predictable error information without manual error serialization in handler code.

Emits structured events for protocol-level operations (initialization, tool calls, resource reads, errors) that can be captured for logging, monitoring, or debugging. Events include timing information, request/response details, and error context, enabling developers to trace execution flow and diagnose issues without modifying handler code.

Provides TypeScript interfaces and type definitions for tool handlers, resource readers, and prompt executors, enabling compile-time type checking of handler signatures and parameter types. Handlers are defined as typed functions that receive validated parameters and return typed results, with IDE autocomplete support for handler registration.

Handles multiple concurrent client requests using Node.js async/await and event-driven architecture, allowing long-running tool executions or resource reads to not block other requests. Each request is processed independently with its own context and error handling, and responses are sent back to clients as they complete.