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How MCP Protocol Handles Tool Discovery: From JSON-RPC Handshake to Enumeration

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The Model Context Protocol (MCP) uses a structured JSON-RPC 2.0 handshake to initiate tool discovery, where clients and servers negotiate protocol versions, transport layers, and supported capabilities before any tools are listed. Clients send an initialize request containing a capabilities object — including flags like supportsToolDiscovery and maxToolCount — and the server responds with its own supported features. Once the handshake is complete, clients issue a tools/list call to enumerate available tools, with production servers using cursor-based pagination to handle large tool registries efficiently. Each tool object returned includes a unique name, a human-readable description, and an inputSchema field that defines parameters using JSON Schema, guiding how language models construct valid tool calls. MCP also supports dynamic filtering during enumeration, allowing clients to narrow tool lists using regular expressions or tag-based selectors, which is particularly useful for agents working within constrained environments.

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How MCP Protocol Handles Tool Discovery: From JSON-RPC Handshake to Enumeration · ShortSingh