Azure Function MCP endpoints 404

Hello Hua, Daniel

Thanks for reaching out on Microsoft Q&A and really appreciate your patience while we looked into this.

From your description, we are sorry to hear you're encountering a 404 error when trying to access the MCP endpoint for your Azure Function.

Suggested steps to Follow:

1. Navigate to your Function App > Overview

 – Ensure the State is Running. If it is Stopped or Failed, click Start.

2. Go to Functions

 – Confirm you see an entry for your MCP streaming function (likely named “mcp” or similar).

 – Click it and inspect Integrate:

  • Verify the Route template is /runtime/webhooks/mcp/sse (host.json override) or that the default routePrefix runtime/webhooks is set and the function’s webHookType (if defined) is mcp.

  • Confirm the Authorization level and that your client code’s code query parameter matches an active function key.

3. Open Advanced Tools (Kudu) > Debug console > site/wwwroot

 – Validate your host.json contains:

  {

   "extensions": {

   "http": {

   "routePrefix": "runtime/webhooks"

   }

   }

  }

 – Validate your function folder (e.g., mcp) contains function.json with the correct bindings including "webHookType": "mcp" or SSE trigger metadata.

4. In Deployment Center

 – Review the last successful deployment timestamp. If a deployment ran just before you saw the 404s, it likely dropped or renamed the function. Consider rolling back or re-deploying the package with your MCP function included.

5. Check App Service logs (if enabled) or Application Insights for any startup errors indicating “failed to load extension” or “cannot deserialize function.json.”

If you're still facing issues after these steps, could you provide a bit more information? Here are some follow-up questions:- Is this the first time you're encountering this 404 error, or has it happened before?

• Have there been any recent deployments or changes made to your Azure Function?
• Are you using any API Management or custom domain that's routing the requests?
• Can you access any other functions within the same Function App?

If you have further questions let us know and also please provide with requested information. Thank you!

@Anonymous The integration tab gives me error:

When I run my MCP servers from my local, I got the following error

#Easy for you to copy
Found Python version 3.12.3 (py).

Azure Functions Core Tools
Core Tools Version:       4.2.1+c3972ebc5fe0738986309e79a6b861828a9812d9 (64-bit)
Function Runtime Version: 4.1041.200.25360

[2025-08-29T15:05:01.361Z] Error downloading zip content https://cdn.functions.azure.com/public/ExtensionBundles/Microsoft.Azure.Functions.ExtensionBundle.Experimental/4.25.1/Microsoft.AzureExtensionBundle.Experimental.4.25.1_any-any.zip. Status Code:NotFound. Reason:The specified blob does not exist.
[2025-08-29T15:05:01.372Z] Unable to find or download extension bundle
[2025-08-29T15:05:01.724Z] No job functions found. Try making your job classes and methods public. If you're using binding extensions (e.g. Azure Storage, ServiceBus, Timers, etc.) make sure you've called the registration method for the extension(s) in your startup code (e.g. builder.AddAzureStorage(), builder.AddServiceBus(), builder.AddTimers(), etc.).

And I can see a new release came out just yesterday

https://github.com/Azure/azure-functions-extension-bundles/releases

Did you just created new release in the Experimental package but forgot to repoint the URL?

sorry, duplicated comment, ignore it

Hello Hua, Daniel,
I hope the provided answer is helpful, do let me know if you have any further questions on this Please accept as Yes if the answer is helpful so that it can help others in the community.
Thanks