Check Existing Issues

• I have searched for any existing and/or related issues.
• I have searched for any existing and/or related discussions.
• I have also searched in the CLOSED issues AND CLOSED discussions and found no related items (your issue might already be addressed on the development branch!).
• I am using the latest version of Open WebUI.

Installation Method

Docker

Open WebUI Version

v0.6.40

Ollama Version (if applicable)

Not relevant to this bug (MCP tools are independent of Ollama)

Operating System

Ubuntu 24.04, macOS 15.1, Windows 11 + WSL2

Browser (if applicable)

Chrome 131, Firefox 132, Edge 131 — identical behavior

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

When adding a new MCP tool (local), Open WebUI should follow the MCP specification for HTTP(S)/SSE transport. The spec explicitly requires:

“The client MUST include an Accept header, listing text/event-stream as a supported content type.”
— https://modelcontextprotocol.io/specification/2025-06-18/basic/transports#listening-for-messages-from-the-server

During validation/connectivity check, Open WebUI should send an Accept header that includes text/event-stream. The request should succeed for spec-compliant servers.

Actual Behavior

During MCP tool validation (when clicking “Save”), Open WebUI sends a GET request with Accept: application/json. The "text/event-stream" value is missing. Spec-compliant MCP servers now typically enforce the Accept header and respond with HTTP 406 Not Acceptable. As a result, valid MCP tools cannot be added — appearing unavailable in the UI.

Steps to Reproduce

1. Run Open WebUI v0.6.40:
2. Start any strict MCP server that requires Accept: text/event-stream (public/private implementations available).
3. In Open WebUI: Go to Settings → external Tools → Add new tool → enter MCP server URL (e.g., http://host.docker.internal:4000/mcp).
4. Click Save.
5. In browser DevTools (Network tab), observe the outgoing GET request:
   • Header sent: Accept: application/json
   • The value "text/event-stream" is absent
6. Server responds: HTTP/1.1 406 Not Acceptable → tool fails to add

All relevant settings and configuration should be included (see context above).

Logs & Screenshots

Request header (browser network tab):
Accept: application/json

Response:
HTTP/1.1 406 Not Acceptable

Open WebUI logs (Docker or backend): Will show tool server unavailable, corresponding to failed validation.

Additional Information

Suggested fix: In the code handling MCP validation/health-check, change the request Accept header to "text/event-stream, application/json" (or simply "text/event-stream"). Bringing this into spec compliance will allow tool registration with all strict MCP servers.

Context: This breaks all strict MCP tool integrations, making compliant server development and testing impossible. Thank you for maintaining Open WebUI!