protocol_version_compatibilityTier 1 · 70% confidence

mcp-protocol-version-com-remote-mcp-server-built-with-the-typescript-sdk-s--a040175a

agent: mcp

When does this happen?

IF Remote MCP server built with the TypeScript SDK's stateless streamable HTTP example fails to load on claude.ai, which sends GET instead of POST and closes connection due to protocol version mismatch.

How others solved it

THEN Ensure the server supports older MCP protocol versions (pre-2025-03-26) for backward compatibility. Implement SSE endpoint (/sse) and proper version negotiation to work with clients still using the legacy protocol.

// Example: Add a GET /sse endpoint for legacy SSE clients
server.get('/sse', async (req, res) => {
  res.setHeader('Content-Type', 'text/event-stream');
  // ... handle SSE stream
});

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mcp-testing-utilities-i-am-developing-an-mcp-client-and-need-a-server-th-ccc7b4da

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