[Librechat] StreamableHTTPError: Streamable HTTP error: Failed to open SSE stream: Not Found

[demian85]

Hi,

I'm trying to setup this server using Librechat, but it cannot connect to the stream.

LibreChat         | 2025-11-20 12:00:49 info: [MCP][postgres] Creating streamable-http transport: http://localhost:3081/mcp
LibreChat         | 2025-11-20 12:00:49 error: [MCP][postgres] Transport error: fetch failed
LibreChat         | 2025-11-20 12:00:49 info: [MCP][postgres] Streamable-http transport closed
LibreChat         | 2025-11-20 12:00:49 error: [MCP][postgres] Connection failed: fetch failed
LibreChat         | 2025-11-20 12:00:53 info: [MCP][postgres] Creating streamable-http transport: http://localhost:3081/mcp
LibreChat         | 2025-11-20 12:00:53 error: [MCP][postgres] Transport error: fetch failed
LibreChat         | 2025-11-20 12:00:53 info: [MCP][postgres] Streamable-http transport closed
LibreChat         | 2025-11-20 12:00:53 error: [MCP][postgres] Connection failed: fetch failed
LibreChat         | 2025-11-20 12:00:53 error: [MCP][postgres] Failed to connect after 3 attempts fetch failed
LibreChat         | 2025-11-20 12:00:53 error: [MCP][postgres] Failed to initialize: fetch failed
LibreChat         | 2025-11-20 12:00:53 info: MCP servers initialized successfully. Added 0 MCP tools.

And even the MCP inspector shows this error, however, tools work. Ping does not respond.

 MCP Inspector is up and running at http://127.0.0.1:6274 🚀
New StreamableHttp connection request
Query parameters: {"url":"http://localhost:3081/mcp","transportType":"streamable-http"}
Created StreamableHttp server transport
Created StreamableHttp client transport
Client <-> Proxy  sessionId: af07266b-ae0a-4bfc-aef4-abb069bc1d6d
Received POST message for sessionId af07266b-ae0a-4bfc-aef4-abb069bc1d6d
Received GET message for sessionId af07266b-ae0a-4bfc-aef4-abb069bc1d6d
Error from MCP server: StreamableHTTPError: Streamable HTTP error: Failed to open SSE stream: Not Found
    at StreamableHTTPClientTransport._startOrAuthSse (file:///Users/demian/.npm/_npx/5a9d879542beca3a/node_modules/@modelcontextprotocol/sdk/dist/esm/client/streamableHttp.js:106:23)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5) {
  code: 404
}
Error from MCP server: StreamableHTTPError: Streamable HTTP error: Failed to open SSE stream: Not Found
    at StreamableHTTPClientTransport._startOrAuthSse (file:///Users/demian/.npm/_npx/5a9d879542beca3a/node_modules/@modelcontextprotocol/sdk/dist/esm/client/streamableHttp.js:106:23)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5) {
  code: 404
}

I'm running dbhub as a service in the docker-compose file from Librechat:

services:
  dbhub:
    image: bytebase/dbhub:latest
    container_name: dbhub
    ports:
      - "3081:3081"
    restart: unless-stopped
    environment:
      - DBHUB_LOG_LEVEL=info
    command: --transport http --port 3081 --readonly --max-rows 100 --dsn "${POSTGRES_URL}"

Logs from dbhub container:

Max rows limit: 100 (from command line argument)

Configuration source: command line argument

Connecting with DSN: postgres://postgres:*******@host.docker.internal:5432/postgres

Successfully connected to PostgreSQL database

Using transport: http

Transport source: command line argument

Running in READ-ONLY mode - only read only queries allowed


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| |  | | |_) | |_| |_   _| |__  

| |  | |  _ <|  _  | | | | '_ \ 

| |__| | |_) | | | | |_| | |_) |

|_____/|____/|_| |_|\__,_|_.__/ 

                                

v0.11.6 [READ-ONLY] - Universal Database MCP Server


Port source: command line argument

DBHub server listening at [http://0.0.0.0:3081⁠](http://0.0.0.0:3081/)

Connect to MCP server at [http://0.0.0.0:3081/mcp⁠](http://0.0.0.0:3081/mcp)

Any ideas what's wrong?

Thanks.

[tianzhou]

Can you paste the Librechat setup screenshot? (I am in the middle of adding docs to Librechat integration)

[demian85]

You mean this part from the librechat.yaml file?

[demian85]

I think the url should be http://dbhub:3081/mcp in my case. I changed it and now the mcp server is added. However, I see the same error over and over:

LibreChat         | 2025-11-20 14:07:03 info: [MCP][postgres] Creating streamable-http transport: http://dbhub:3081/mcp
LibreChat         | 2025-11-20 14:07:03 info: [MCP][postgres] Streamable-http transport closed
LibreChat         | 2025-11-20 14:07:03 error: [MCP][postgres] Transport error: This operation was aborted
LibreChat         | 2025-11-20 14:07:03 info: [MCP][postgres] Reconnecting 1/3 (delay: 2000ms)
LibreChat         | 2025-11-20 14:07:03 error: [MCP][postgres] Transport error: This operation was aborted
LibreChat         | 2025-11-20 14:07:03 info: [MCP][postgres] Creating streamable-http transport: http://dbhub:3081/mcp
LibreChat         | 2025-11-20 14:07:03 error: [MCP][postgres] Transport error: Streamable HTTP error: Failed to open SSE stream: Not Found
LibreChat         | 2025-11-20 14:07:03 info: [MCP][postgres] Reconnecting 1/3 (delay: 2000ms)
LibreChat         | 2025-11-20 14:07:03 error: [MCP][postgres] Transport error: Streamable HTTP error: Failed to open SSE stream: Not Found
LibreChat         | 2025-11-20 14:07:05 info: [MCP][postgres] Streamable-http transport closed
LibreChat         | 2025-11-20 14:07:05 info: [MCP][postgres] Creating streamable-http transport: http://dbhub:3081/mcp
LibreChat         | 2025-11-20 14:07:05 info: [MCP][postgres] Streamable-http transport closed
LibreChat         | 2025-11-20 14:07:05 error: [MCP][postgres] Transport error: This operation was aborted
LibreChat         | 2025-11-20 14:07:05 info: [MCP][postgres] Creating streamable-http transport: http://dbhub:3081/mcp
LibreChat         | 2025-11-20 14:07:05 info: [MCP][postgres] Streamable-http transport closed
LibreChat         | 2025-11-20 14:07:05 error: [MCP][postgres] Connection failed: This operation was aborted
LibreChat         | 2025-11-20 14:07:05 error: [MCP][postgres] Reconnection attempt failed: This operation was aborted
LibreChat         | 2025-11-20 14:07:05 info: [MCP][postgres] Reconnecting 2/3 (delay: 4000ms)
LibreChat         | 2025-11-20 14:07:05 error: [MCP][postgres] Connection failed: Not connected
LibreChat         | 2025-11-20 14:07:05 error: [MCP][postgres] Reconnection attempt failed: Not connected
LibreChat         | 2025-11-20 14:07:05 info: [MCP][postgres] Reconnecting 3/3 (delay: 8000ms)
LibreChat         | 2025-11-20 14:07:09 info: [MCP][postgres] Creating streamable-http transport: http://dbhub:3081/mcp
LibreChat         | 2025-11-20 14:07:09 error: [MCP][postgres] Transport error: Streamable HTTP error: Failed to open SSE stream: Not Found

[demian85]

Confirmed, the mcp integration now works, but I keep seeing those errors in the console over and over. They never stop as if the service is trying to reconnect forever.
Not sure if it's a Librechat issue or dbhub issue.

[demian85]

Well, I'm back again. The server does not seem to work properly though since Librechat is too slow with the stream. It takes ages to receive a response as if the connection closes and reopens multiple times forever. Something is off.
Using "sse" type in the librechat.yaml config does not work.
I see in the source this line of code that may be breaking things: enableJsonResponse: false // Use SSE streaming