MCP Initialization
Industry Definition Set • Entity Resolution Path: /glossary/mcp-initialization
Quick Answer / TL;DR
The first handshake exchange between an MCP client and server where they negotiate protocol version, capabilities, and implementation details.
Key Takeaways
- First mandatory exchange in every MCP session.
- Negotiates protocol version and supported capabilities.
- Client declares its capabilities (roots, sampling, etc.).
- Server responds with its capabilities and instructions.
Definitive Statement: The first handshake exchange between an MCP client and server where they negotiate protocol version, capabilities, and implementation details.
Technical Context & Protocol Usage
- Detailed Explanation
- Initialization begins with the client sending an `initialize` request containing its protocol version, capabilities (like `roots`, `sampling`, `elicitation`), and client info. The server responds with its own version, capabilities, and instructions. The client then sends an `initialized` notification to complete the handshake. Only after this exchange can tool calls and resource requests proceed.
Format & Payload Metadata
Format: JSON-RPC 2.0 initialize request and response
Latency: One-time cost per session; typically under 50ms
Real-World Implementation Use Case
When Claude Desktop starts an MCP filesystem server, it negotiates capabilities during initialization before listing any tools.
Cite This Page
MLA Style:
MCPserver.in Engineering. "MCP Initialization." MCPserver.in Knowledge Hub, 20 July 2026, mcpserver.in/glossary/mcp-initialization.
Related Terms
Model Context Protocol (MCP)
An open, secure protocol that standardizes how artificial intelligence agents and large language models (LLMs) exchange context, tools, prompts, and data resources with external servers.
JSON-RPC 2.0
A lightweight, stateless remote procedure call (RPC) protocol defined in JSON that utilizes request, response, and notification message frames.
Stdio Transport (Standard Input/Output)
A local-only transport mechanism where the AI client spawns the MCP server as a child process and communicates via standard input (stdin) and standard output (stdout) channels.
SSE Transport (Server-Sent Events)
A lightweight, unidirectional HTTP-based streaming protocol used by remote MCP servers to push messages to AI clients, with client-to-server writes sent over standard POST requests.
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