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mcp-protocol-server-implementation

Fix MCP server initialization and transport compatibility for SDK clients.

Updated Nov 18, 2025
Search Tags:#protocol#mcp#server#cors#sse#initialize#streamable http
One-click install
npx skills add https://github.com/cajias/claude-skills --skill mcp-protocol-server-implementation
Or copy as Structured Prompt for Agent▼
Please help me install this Agent Skill.
Skill: mcp-protocol-server-implementation
Source: https://github.com/cajias/claude-skills/tree/main/skills/mcp-protocol-server-implementation
Command: npx skills add https://github.com/cajias/claude-skills --skill mcp-protocol-server-implementation

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve?

This Skill helps you fix MCP server connection failures, especially cases where a custom server returns valid tool data but the official Claude or MCP SDK client cannot initialize, times out, or reports an expected response error.

Core Features & Use Cases

  • Initialize handling: Ensures the server responds correctly to the mandatory initialize request with the right protocol version, server info, and tool capabilities.
  • Notification support: Covers proper handling of notifications such as initialized messages, which must not receive a response body.
  • Transport and session compatibility: Provides guidance for Streamable HTTP, SSE formatting, session IDs, and required CORS headers so browser and SDK clients can connect successfully.
  • Use case: Use this Skill when building an MCP server from scratch or debugging a server that works with curl but fails in the official SDK client.

Quick Start

Ask Claude to review your MCP server implementation and tell you exactly how to handle initialize, notifications, SSE, session headers, and CORS so the official SDK client can connect.

Frequently Asked Questions about mcp-protocol-server-implementation

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
Why does my MCP server time out when the official SDK client tries to connect?▼

MCP server timeouts typically occur when the initialize response lacks the correct protocol version, server info, or tool capabilities. The server must also properly handle initialized notifications without returning a response body.

How do I fix an MCP server that works with curl but fails in the official Claude client?▼

If your MCP server works with curl but fails in the official client, check your SSE formatting, session ID management, and CORS headers. Browser and SDK clients require specific transport configurations that curl does not enforce.

What does an MCP server need to return for the initialize request?▼

For the initialize request, an MCP server must return the correct protocol version, server information, and tool capabilities. This ensures the official SDK client can properly recognize and establish the connection.

Do I need to configure CORS headers for an MCP server using Streamable HTTP?▼

Yes, configuring CORS headers is required for MCP servers using Streamable HTTP transport. Correct CORS headers allow browser and SDK clients to successfully connect to your server without cross-origin issues.

How should an MCP server handle initialized notifications from the client?▼

An MCP server must properly handle initialized notifications by acknowledging them without sending a response body. Failing to omit the response body can cause the official SDK client to report an unexpected response error.

What is the best way to debug MCP server transport compatibility issues?▼

The best way to debug MCP server transport compatibility is to validate SSE formatting, session ID management, and required CORS headers. This ensures reliable connections between custom servers and official SDK clients.

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