issue: OK with SSE / KO with Streamable http

[chdid]

Check Existing Issues

• I have searched the existing issues and discussions.
• I am using the latest version of Open WebUI.

Installation Method

Docker

Open WebUI Version

0.6.18

Ollama Version (if applicable)

No response

Operating System

docker

Browser (if applicable)

firefox chrome

Confirmation

• I have read and followed all instructions in README.md.
• I am using the latest version of both Open WebUI and Ollama.
• I have included the browser console logs.
• I have included the Docker container logs.
• I have provided every relevant configuration, setting, and environment variable used in my setup.
• I have clearly listed every relevant configuration, custom setting, environment variable, and command-line option that influences my setup (such as Docker Compose overrides, .env values, browser settings, authentication configurations, etc).
• I have documented step-by-step reproduction instructions that are precise, sequential, and leave nothing to interpretation. My steps:
• Start with the initial platform/version/OS and dependencies used,
• Specify exact install/launch/configure commands,
• List URLs visited, user input (incl. example values/emails/passwords if needed),
• Describe all options and toggles enabled or changed,
• Include any files or environmental changes,
• Identify the expected and actual result at each stage,
• Ensure any reasonably skilled user can follow and hit the same issue.

Expected Behavior

Proxy with streamable http

Actual Behavior

Proxy OK with SSE version of https://github.com/antvis/mcp-server-chart
But KO with streamable_http

Steps to Reproduce

• Install the server in Docker: https://hub.docker.com/r/acuvity/mcp-server-chart
• Install the OpenWebUI proxy - MCP in Docker: https://github.com/open-webui/mcpo
• Configure the MCP server in SSE on MCPO:
  {
  "mcpServers": {
  "chart": {
  "type": "sse",
  "url": "http://xxxxxxxx:8006/sse"
  }
  }
  }

=> MCPO OK / swagger OK

In streamable http
{
"mcpServers": {
"chart": {
"type": "streamable_http",
"url": "http://xxxxxxxx:8006/mcp"
}
}
}

=> MCPO KO

Logs & Screenshots

Starting MCP OpenAPI Proxy with config file: /config/config.json

2025-07-21 07:53:29,595 - INFO - Starting MCPO Server...

2025-07-21 07:53:29,595 - INFO - Name: MCP OpenAPI Proxy

2025-07-21 07:53:29,595 - INFO - Version: 1.0

2025-07-21 07:53:29,595 - INFO - Description: Automatically generated API from MCP Tool Schemas

2025-07-21 07:53:29,595 - INFO - Hostname: d3f0777bc4f8

2025-07-21 07:53:29,595 - INFO - Port: 8000

2025-07-21 07:53:29,595 - INFO - API Key: Not Provided

2025-07-21 07:53:29,595 - INFO - CORS Allowed Origins: ['*']

2025-07-21 07:53:29,596 - INFO - Path Prefix: /

2025-07-21 07:53:29,596 - INFO - Loading MCP server configurations from: /config/config.json

2025-07-21 07:53:29,596 - INFO - Configured MCP Servers:

2025-07-21 07:53:29,596 - INFO - Configuring StreamableHTTP MCP Server 'chart' with URL: http://XXX:8006/mcp

2025-07-21 07:53:29,597 - INFO - Uvicorn server starting...

INFO: Started server process [1]

INFO: Waiting for application startup.

2025-07-21 07:53:29,661 - INFO - HTTP Request: POST http://XXX:8006/mcp/ "HTTP/1.1 404 Not Found"

ERROR: + Exception Group Traceback (most recent call last):

| File "/app/.venv/lib/python3.11/site-packages/starlette/routing.py", line 692, in lifespan

| async with self.lifespan_context(app) as maybe_state:

| File "/usr/lib/python3.11/contextlib.py", line 204, in aenter

| return await anext(self.gen)

| ^^^^^^^^^^^^^^^^^^^^^

| File "/app/.venv/lib/python3.11/site-packages/mcpo/main.py", line 102, in lifespan

| await stack.enter_async_context(

| File "/usr/lib/python3.11/contextlib.py", line 638, in enter_async_context

| result = await _enter(cm)

| ^^^^^^^^^^^^^^^^

| File "/usr/lib/python3.11/contextlib.py", line 204, in aenter

| return await anext(self.gen)

| ^^^^^^^^^^^^^^^^^^^^^

| File "/app/.venv/lib/python3.11/site-packages/mcpo/main.py", line 140, in lifespan

| async with streamablehttp_client(url=url, headers=headers) as (

| File "/usr/lib/python3.11/contextlib.py", line 222, in aexit

| await self.gen.athrow(typ, value, traceback)

| File "/app/.venv/lib/python3.11/site-packages/mcp/client/streamable_http.py", line 474, in streamablehttp_client

| async with anyio.create_task_group() as tg:

| File "/app/.venv/lib/python3.11/site-packages/anyio/_backends/_asyncio.py", line 772, in aexit

| raise BaseExceptionGroup(

| ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)

+-+---------------- 1 ----------------

| Exception Group Traceback (most recent call last):

|   File "/app/.venv/lib/python3.11/site-packages/mcp/client/streamable_http.py", line 498, in streamablehttp_client

|     yield (

|   File "/app/.venv/lib/python3.11/site-packages/mcpo/main.py", line 145, in lifespan

|     async with ClientSession(reader, writer) as session:

|   File "/app/.venv/lib/python3.11/site-packages/anyio/_backends/_asyncio.py", line 772, in __aexit__

|     raise BaseExceptionGroup(

| ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)

+-+---------------- 1 ----------------

  | Traceback (most recent call last):

  |   File "/app/.venv/lib/python3.11/site-packages/mcpo/main.py", line 147, in lifespan

  |     await create_dynamic_endpoints(app, api_dependency=api_dependency)

  |   File "/app/.venv/lib/python3.11/site-packages/mcpo/main.py", line 30, in create_dynamic_endpoints

  |     result = await session.initialize()

  |              ^^^^^^^^^^^^^^^^^^^^^^^^^^

  |   File "/app/.venv/lib/python3.11/site-packages/mcp/client/session.py", line 151, in initialize

  |     result = await self.send_request(

  |              ^^^^^^^^^^^^^^^^^^^^^^^^

  |   File "/app/.venv/lib/python3.11/site-packages/mcp/shared/session.py", line 286, in send_request

  |     raise McpError(response_or_error.error)

  | mcp.shared.exceptions.McpError: Session terminated

  +------------------------------------

ERROR: Application startup failed. Exiting.

Additional Information

No response

[taylorwilsdon]

Hey there, few questions to help ya out:

• what version of MCPO are you using?
• any logs from the streamable HTTP MCP itself?
• was the MCP still running and accessible through another client (ie mcp inspector) after mcpo reported the above?

[chdid]

what version of MCPO are you using?
The last one from ghcr.io/open-webui/mcpo:main.
I see in the log
2025-07-22 05:26:13,504 - INFO - Name: MCP OpenAPI Proxy
2025-07-22 05:26:13,504 - INFO - Version: 1.0

any logs from the streamable HTTP MCP itself?

No error from server MCP.

Jul 22 05:29:09 INF Policer configured type=rego policy=/policy.rego enforced=true

Jul 22 05:29:09 INF SBOM configured tools=22 prompts=0

Jul 22 05:29:09 INF MCP server configured mode=stdio command=/app/node_modules/.bin/mcp-server-chart args=[]

Jul 22 05:29:09 INF Metrics manager configured listen=:8080 health=/ metrics=/metrics

Jul 22 05:29:09 INF Minibridge frontend configured mcp=/mcp sse=/sse messages=/message agent-token=false mode=http server-tls=false server-mtls=NoClientCert listen=:8000

Jul 22 05:29:09 INF Minibridge backend configured

Jul 22 05:29:09 INF OAuth authentication dance is disabled

was the MCP still running and accessible through another client (ie mcp inspector) after mcpo reported the above?

Yes. Screenshot above from mcp inspector

[taylorwilsdon]

The error you're getting from mcpo is a flat out 404 so without being able to compare the actual urls which have been redacted, my best guess is that your client running mcp inspector can reach the streamable http endpoint but whenever mcpo is running can't.

The new version of mcpo in dev allows graceful failures so at least it won't crash from a 404 but this is either a typo in the url or a network path issue, impossible to say without more info

2025-07-21 07:53:29,596 - INFO - Configuring StreamableHTTP MCP Server 'chart' with URL: http://XXX:8006/mcp

2025-07-21 07:53:29,597 - INFO - Uvicorn server starting...

INFO: Started server process [1]

INFO: Waiting for application startup.

2025-07-21 07:53:29,661 - INFO - HTTP Request: POST http://XXX:8006/mcp/ "HTTP/1.1 404 Not Found"

[matanrom]

I encountered the same problem.
It seems like mcpo is adding tailing slash to StreamableHTTP which may make some servers to return 404.
For example "https://mcp.context7.com/mcp" will return 200 while "https://mcp.context7.com/mcp/" will return 404.

[chdid]

The error you're getting from mcpo is a flat out 404 so without being able to compare the actual urls which have been redacted, my best guess is that your client running mcp inspector can reach the streamable http endpoint but whenever mcpo is running can't.

The new version of mcpo in dev allows graceful failures so at least it won't crash from a 404 but this is either a typo in the url or a network path issue, impossible to say without more info

2025-07-21 07:53:29,596 - INFO - Configuring StreamableHTTP MCP Server 'chart' with URL: http://XXX:8006/mcp

2025-07-21 07:53:29,597 - INFO - Uvicorn server starting...

INFO: Started server process [1]

INFO: Waiting for application startup.

2025-07-21 07:53:29,661 - INFO - HTTP Request: POST http://XXX:8006/mcp/ "HTTP/1.1 404 Not Found"

Thank you. But http://XXX:8006/sse is OK on the same server. MCPO has no network problem.

"For example "https://mcp.context7.com/mcp" will return 200 while "https://mcp.context7.com/mcp/" will return 404."
=> I have the same result.

[mrkmrtns]

Same issue.
Problem is that mcpo adds trailing / although it's not specified.
Looks like bug to me and is issue with using many MCP servers.

If I add trailing / in my own mcp server path in first place then it works, but in many cases it's not under Your control. It should honor the path as set with url.

It probably comes from here:

mcpo/src/mcpo/main.py

Line 137 in 1986204

url = f"{url}/"

Maybe there is some other solution to this as this one makes it unusable with many MCP servers out there or make that behavior configurable.

[taylorwilsdon]

Interesting - I have not had any issues with that, and the spec actually calls for a trailing slash:
https://gofastmcp.com/deployment/running-server#streamable-http

That's likely why the url rewrite was there, because the original spec calls for path (/mcp/)
It sounds like whatever mcp you're using with streamable http is not handling that appropriately. FWIW the official hosted Context7 works fine with trailing slash (/)

I've gone ahead and removed the url = f"{url}/" from the dev branch because either way it's not necessary. Give it a try @mrkmrtns @chdid @matanrom (the dev build) and let me know if that resolves your issues, we'll have a new release out shortly.

[mrkmrtns]

@taylorwilsdon just tested with dev branch. Now works without trailing slash also correctly.

Thank You!

[taylorwilsdon]

Great, we'll get that released perhaps today!

[taylorwilsdon]

Released, let me know if you have any issues!