@modelcontextprotocol/express

Provides Express middleware adapters that expose Model Context Protocol servers over HTTP, translating incoming HTTP requests to MCP protocol messages and routing them to the appropriate server handlers. Uses Express routing patterns to map HTTP endpoints to MCP resource and tool operations, enabling REST-like access to MCP capabilities through standard HTTP verbs and JSON payloads.

Translates between MCP protocol message formats (resources, tools, prompts) and HTTP request/response semantics, mapping MCP operations like resource reads, tool invocations, and prompt completions to HTTP endpoints with appropriate methods and status codes. Handles bidirectional serialization of MCP types (TextContent, ImageContent, ToolResult) into JSON-compatible HTTP payloads.

Routes HTTP POST requests to MCP tool definitions, validates input parameters against tool schemas, invokes the underlying tool handler, and returns structured results as HTTP responses. Implements parameter binding from HTTP request bodies to tool function signatures, with support for complex argument types and error handling that maps tool execution failures to appropriate HTTP status codes.

Exposes MCP resources as HTTP endpoints, mapping resource URIs to HTTP GET requests and serving resource content with appropriate Content-Type headers. Implements content negotiation for resources that support multiple MIME types (e.g., text vs. binary), and handles resource metadata (size, modification time) as HTTP headers. Supports both simple text resources and complex content types through proper HTTP serialization.

Exposes MCP prompt definitions as HTTP endpoints, allowing clients to request prompt templates with variable substitution. Implements parameter binding from HTTP request bodies or query strings to prompt template variables, renders the prompt with provided arguments, and returns the rendered prompt as HTTP JSON responses. Supports both simple text prompts and complex multi-argument prompts with validation.

Maps MCP protocol errors and exceptions to appropriate HTTP status codes and error response formats, translating MCP error types (InvalidRequest, InternalError, etc.) to HTTP semantics (400, 500, etc.). Implements Express error middleware that catches MCP-specific exceptions and formats them as JSON error responses with error codes, messages, and optional stack traces for debugging.

Enables composition of Express middleware with MCP protocol handling, allowing developers to add authentication, logging, rate limiting, and other cross-cutting concerns to MCP HTTP endpoints. Implements middleware chaining patterns where MCP protocol translation occurs as a middleware step, allowing other middleware to execute before/after protocol handling. Supports both pre-processing (auth, validation) and post-processing (logging, response transformation) middleware.

Provides TypeScript type definitions and interfaces for MCP HTTP adapter, enabling compile-time type checking of MCP server configurations, request handlers, and response objects. Implements generic types for tool invocations, resource access, and prompt rendering that enforce type safety across the HTTP boundary. Supports type inference from MCP server definitions to catch type mismatches at compile time rather than runtime.