Kuberwastaken/claurst · error

rmcp client ' ' failed to initialize

Error message

rmcp {} client '{}' failed to initialize: {}

What it means

The rmcp client failed during the MCP `initialize` handshake over the labelled transport (stdio, streamable-http, or sse). The connection was established but the protocol negotiation/initialization round-trip failed — version mismatch, the peer not speaking MCP, or the connection dropping during init.

Solutions

1. Verify the remote is a real MCP server speaking a compatible protocol version
2. Check server logs for why initialization was rejected
3. Confirm the server did not exit or close the connection immediately after accept

When it happens

Trigger: Thrown at src-rust/crates/mcp/src/rmcp_backend.rs:177 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of Kuberwastaken/claurst@b0637c97ec (2026-09-10). Data as JSON: /api/errors/aeda383a6843cd94. Report an issue: GitHub.

Appendix: source

Thrown at src-rust/crates/mcp/src/rmcp_backend.rs:177

        let transport = LegacySseRmcpTransport::connect(config, auth_token).await?;
        let client_info = build_client_info(rmcp_model::ProtocolVersion::V_2024_11_05);
        Self::connect_with_transport(config, transport, client_info, "sse").await
    }

    async fn connect_with_transport<T, E, A>(
        config: &claurst_core::config::McpServerConfig,
        transport: T,
        client_info: rmcp_model::ClientInfo,
        transport_label: &str,
    ) -> anyhow::Result<Self>
    where
        T: rmcp::transport::IntoTransport<RoleClient, E, A>,
        E: std::error::Error + Send + Sync + 'static,
    {
        let (notifications_tx, notifications_rx) = mpsc::unbounded_channel();
        let handler = RmcpNotificationClient::new(notifications_tx, client_info);
        let running = handler.serve(transport).await.map_err(|e| {
            anyhow::anyhow!(
                "rmcp {} client '{}' failed to initialize: {}",
                transport_label,
                config.name,
                e
            )
        })?;

        let peer = running.peer().clone();
        let snapshot = build_snapshot(config, &peer).await?;

        Ok(Self {
            snapshot,
            peer,
            running: Mutex::new(running),
            notifications_rx: Arc::new(Mutex::new(notifications_rx)),
        })
    }
}

View on GitHub (pinned to b0637c97ec)