protocol_version_mismatchTier 1 · 70% confidence

mcp-protocol-version-mis-mcp-inspector-fails-to-connect-to-a-streamable-htt-9a46d41d

agent: mcp

When does this happen?

IF MCP inspector fails to connect to a Streamable HTTP server that advertises protocol version 2025-03-26, because the TypeScript SDK's LATEST_PROTOCOL_VERSION is still set to 2024-11-05.

How others solved it

THEN Update the `LATEST_PROTOCOL_VERSION` constant in the TypeScript SDK's `src/types.ts` file to the latest protocol version supported by your MCP server (e.g., `'2025-03-26'`). Alternatively, upgrade to the latest SDK version that includes this fix. This ensures the client and server negotiate the correct protocol version.

export const LATEST_PROTOCOL_VERSION = '2025-03-26';

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