SSE MCP Server works perfectly but Claude Web Interface won't connect - Need help with browser extension workaround

[JanyaBayana]

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Question Category

• Protocol Specification
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Your Question

Background:
I've built a MCP server using Python Flask that exposes some data through MCP tools. The server implements SSE (Server-Sent Events) transport and is fully functional - all the JSON-RPC protocols are working correctly, authentication passes, and tools are properly listed.

Technical Details:
Server: Python Flask with SSE endpoint at /{token}/sse
Transport: HTTP with Server-Sent Events (SSE)
Protocol: MCP 2024-11-05 compliant
Authentication: Token-based with Firestore backend
Tools: account listing, property querying, quota management

The Problem:
My logs show everything working perfectly:
-> Successful MCP handshake (initialize method)
-> Proper tool listing (tools/list returns correct schema)
-> Authentication working (user resolved from token)
-> JSON-RPC 2.0 compliant responses

But Claude's web interface simply won't connect.

What I'm Looking For:

1. Has anyone successfully used the claude-mcp browser extension mentioned in the codemcp project to connect SSE MCP servers to Claude's web interface?
2. Are there other community workarounds for connecting web Claude to remote MCP servers?

Any guidance would be greatly appreciated!

[benjaminbelaga]

Hey! I've been running a remote MCP server in production for a few weeks now (Google Workspace integration), so I can share what works.

The core issue

Claude's web interface (claude.ai) doesn't support connecting to custom/remote MCP servers directly. This is by design - the web UI only connects to Anthropic's own MCP integrations.

What actually works for remote MCP servers

1. Claude Desktop App (macOS/Windows)

This is the official way to connect remote MCP servers. Add your server to ~/Library/Application Support/Claude/claude_desktop_config.json:

{
  "mcpServers": {
    "your-server": {
      "url": "https://your-domain.com/mcp",
      "transport": "sse"
    }
  }
}

2. Claude Code (CLI)

Configure in ~/.claude/mcp.json:

{
  "mcpServers": {
    "your-server": {
      "type": "url",
      "url": "https://your-domain.com/{token}/sse"
    }
  }
}

3. Browser extensions

The claude-mcp browser extension is experimental and not officially supported. I wouldn't rely on it for production use.

Quick debugging checklist

Since your server logs look good, verify these:

1. CORS headers - Make sure your Flask app returns proper CORS headers for the SSE endpoint
2. SSL/TLS - Remote MCP requires HTTPS (no self-signed certs)
3. Content-Type - SSE responses need text/event-stream
4. Keep-alive - Your server/proxy shouldn't timeout the SSE connection

My setup (working)

- FastMCP on VPS behind Nginx reverse proxy
- Let's Encrypt SSL
- Systemd for process management
- Works perfectly with Claude Code CLI

Hope this helps! The key insight is: web interface ≠ remote MCP support. Use Desktop or CLI.