How MCP Works: The Complete Request Flow

Article is part of a six-part MCP series, part 3 of a six-part MCP article series explaining request flow.

Request flow routes a user query from Host to LLM, through Client and Server, and back to the user, sequence showing user question routed through Host, Client, Server, and back.

LLM tells the Host which capability to call rather than calling tools directly, the LLM selects capabilities but does not directly access external systems.

MCP Server translates requests into native database queries or API calls and returns results, the Server translates MCP requests into native queries or API calls.

MCP messages use JSON-RPC 2.0 Request, Response, and Notification types, mCP builds on JSON-RPC 2.0 message types.