MCP Protocol Version Mismatch in Claude — Fix (2026)

The Error

MCP protocol version mismatch: client v2024-11-05, server v2024-09-01

The Fix

# Update the MCP server SDK to match the client's expected version
cd your-mcp-server/
npm update @modelcontextprotocol/sdk
# Or install the specific version that supports the protocol:
npm install @modelcontextprotocol/sdk@latest

Why This Works

The Model Context Protocol uses versioned handshakes. Claude Code’s MCP client advertises its protocol version during initialization. If the server responds with an older protocol version, the client rejects the connection because message formats and capabilities differ between versions. Updating the server SDK brings it to the same protocol version the client expects.

If That Doesn’t Work

# Check what protocol version your server is advertising
grep -r "protocolVersion\|protocol_version" your-mcp-server/node_modules/@modelcontextprotocol/
# If using a custom server, update the version in your implementation:
# In your server initialization code, set:
#   protocolVersion: "2024-11-05"
# Or downgrade Claude Code if you cannot update the server:
npm install -g @anthropic-ai/claude-code@previous-version

Pin both client and server to compatible versions if you cannot update the server-side dependency.

Prevention

Add to your CLAUDE.md:

Pin MCP server SDK versions explicitly in package.json. When updating Claude Code, also update all MCP server dependencies. Check protocol compatibility in the MCP changelog before upgrading either side.

See Also

This fix also applies if you see these related error messages:

  • npm ERR! code EACCES
  • npm ERR! code ERESOLVE
  • npm ERR! peer dep missing
  • ETIMEDOUT: connection timed out
  • RequestTimeout: request took longer than 120000ms

Frequently Asked Questions

Should I use npm or pnpm with Claude Code?

Claude Code works with any Node.js package manager. If your project uses pnpm, add Use pnpm instead of npm for all package operations to your CLAUDE.md so Claude Code respects your toolchain choice.

Why does Claude Code sometimes run npm commands that fail?

Claude Code infers the package manager from lock files. If both package-lock.json and pnpm-lock.yaml exist, it may pick the wrong one. Delete the unused lock file or add an explicit instruction in CLAUDE.md.

How do I verify my npm installation is working?

Run npm doctor to check your npm environment. It validates the registry connection, permissions, cache integrity, and Node.js compatibility in one command.

What is the default timeout for Claude Code API requests?

The default timeout is 120 seconds (120000ms). For complex operations involving large codebases or multi-file edits, this may be insufficient. Increase it with claude config set api_timeout 300000 for a 5-minute timeout.

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MCP Server Architecture

The Model Context Protocol (MCP) provides a standardized way for Claude Code to interact with external tools and data sources. Understanding the architecture helps diagnose connection issues:

Transport layer. MCP servers communicate with Claude Code over stdio (standard input/output) or HTTP. Stdio is the default and most reliable transport. HTTP transport is used for remote servers.

Initialization handshake. When Claude Code starts, it spawns each configured MCP server as a child process and waits for the initialization response. If this handshake does not complete within 30 seconds, the connection times out.

Tool registration. After initialization, the MCP server declares its available tools (capabilities). Claude Code adds these to its tool catalog. Each registered tool adds approximately 50-100 tokens to the system prompt.

Debugging MCP Connection Issues

Run this diagnostic sequence to isolate MCP problems:

# 1. Test the server command directly
npx -y @modelcontextprotocol/server-filesystem /tmp 2>&1 | head -5
# 2. Check if the port is already in use (HTTP transport)
lsof -i :3100 2>/dev/null
# 3. Verify the config file location and syntax
cat ~/.claude/settings.json | python3 -m json.tool
# 4. Check Claude Code's MCP status
claude -p "/mcp" --trust --yes 2>&1

If the server starts manually but fails in Claude Code, the issue is usually PATH differences between your shell and the spawned subprocess.