a valid MCP initialize was answered with HTTP 404, so no MCP server was found at the address the operator registered.

HTTP 404, body is not a JSON-RPC message


JSON-RPC-ish reply, not a discover result (code=None, error is dict)


a valid MCP initialize was answered with HTTP 400.


the address answered HTTP 200 but the initialize response carried no result

JSON-RPC-ish reply, not a discover result (code=-32001, error is dict)


JSON-RPC-ish reply, not a discover result (code=None, error is str)


HTTP 400, body is not a JSON-RPC message


JSON-RPC-ish reply, not a discover result (code=-32600, error is dict)


method not found (-32601): server/discover is MUST in 2026-07-28


a valid MCP initialize was answered with HTTP 410, so no MCP server was found at the address the operator registered.

HTTP 410, body is not a JSON-RPC message


JSON-RPC-ish reply, not a discover result (code=-32603, error is dict)


a valid MCP initialize was answered with HTTP 421.

HTTP 421, body is not a JSON-RPC message


not reached: URLError / ConnectionRefusedError / errno 61 / [Errno 61] Connection refused


HTTP 422, body is not a JSON-RPC message


HTTP 200, body is not a JSON-RPC message


a valid MCP initialize was answered with HTTP 500.

HTTP 500, body is not a JSON-RPC message


a valid MCP initialize was answered with HTTP 429.

JSON-RPC-ish reply, not a discover result (code=-32000, error is dict)


HTTP 307, body is not a JSON-RPC message


JSON-RPC-ish reply, not a discover result (code=None, no error field)


HTTP 404, body is not a JSON-RPC message


HTTP 429, body is not a JSON-RPC message


JSON-RPC-ish reply, not a discover result (code=-32001, error is dict)


JSON-RPC-ish reply, not a discover result (code=None, error is dict)


JSON-RPC-ish reply, not a discover result (code=None, error is str)


JSON-RPC-ish reply, not a discover result (code=-32600, error is dict)


a valid MCP initialize was answered with HTTP 308.

HTTP 308, body is not a JSON-RPC message


HTTP 400, body is not a JSON-RPC message


HTTP 405, body is not a JSON-RPC message


JSON-RPC-ish reply, not a discover result (code=-32603, error is dict)


method not found (-32601): server/discover is MUST in 2026-07-28


HTTP 530, body is not a JSON-RPC message


HTTP 200, body is not a JSON-RPC message


not reached: URLError / ConnectionResetError / errno 54 / [Errno 54] Connection reset by peer


HTTP 410, body is not a JSON-RPC message


HTTP 422, body is not a JSON-RPC message


HTTP 500, body is not a JSON-RPC message


HTTP 404, body is not a JSON-RPC message


HTTP 307, body is not a JSON-RPC message


JSON-RPC-ish reply, not a discover result (code=-32001, error is dict)


JSON-RPC-ish reply, not a discover result (code=None, error is dict)


JSON-RPC-ish reply, not a discover result (code=-32602, error is dict)


JSON-RPC-ish reply, not a discover result (code=None, error is str)


HTTP 308, body is not a JSON-RPC message


HTTP 400, body is not a JSON-RPC message


JSON-RPC-ish reply, not a discover result (code=-32000, error is dict)


JSON-RPC-ish reply, not a discover result (code=-32600, error is dict)


HTTP 401, body is not a JSON-RPC message


JSON-RPC-ish reply, not a discover result (code=-32603, error is dict)


method not found (-32601): server/discover is MUST in 2026-07-28


HTTP 200, body is not a JSON-RPC message


modern JSON-RPC error -32022 (UnsupportedProtocolVersion)


a valid MCP initialize was answered with HTTP 307.


not reached: timeout / The read operation timed out


HTTP 410, body is not a JSON-RPC message


HTTP 404, body is not a JSON-RPC message


HTTP 429, body is not a JSON-RPC message


HTTP 421, body is not a JSON-RPC message


HTTP 500, body is not a JSON-RPC message


JSON-RPC-ish reply, not a discover result (code=None, error is dict)


JSON-RPC-ish reply, not a discover result (code=None, error is str)


HTTP 422, body is not a JSON-RPC message


HTTP 307, body is not a JSON-RPC message


HTTP 400, body is not a JSON-RPC message


HTTP 308, body is not a JSON-RPC message


JSON-RPC-ish reply, not a discover result (code=-32001, error is dict)


JSON-RPC-ish reply, not a discover result (code=None, no error field)


JSON-RPC-ish reply, not a discover result (code=-32602, error is dict)


JSON-RPC-ish reply, not a discover result (code=-32600, error is dict)


HTTP 200, body is not a JSON-RPC message