Fix “Functions:Worker:HostEndpoint” missing in Azure Functions (.NET Isolated)

Recently, I was trying to run an Azure Function locally in my Visual Studio 2020 environment, and while trying to run, I got the following error:

System.InvalidOperationException: ‘Configuration is missing the ‘HostEndpoint’ information. Please ensure an entry with the key ‘Functions:Worker:HostEndpoint’ is present in your configuration.’

…you’re almost certainly running a .NET Isolated Azure Functions project in a way that starts the worker but not the Functions host.

Good news: this is usually a launch/config mismatch, not a code bug.

Cause

In the .NET Isolated model, your function app is split into two processes:

• Azure Functions Host (the runtime host that loads triggers, bindings, routes, etc.)
• .NET Worker (your .NET process that runs your function code)

The HostEndpoint is the connection info that the host provides to the worker at startup so they can talk to each other.

So when you see this exception, it typically means:

• ✅ Your worker started
• ❌ The Azure Functions host did not
• ➡️ Therefore, the worker never received Functions:Worker:HostEndpoint

Functions:Worker:HostEndpoint is injected by the Functions host at startup; if the host isn’t running (or VS is launching the wrong profile), the worker can’t connect, and you get this error.

Solution

To solve this, we need to fix our local dev by ensuring the following steps:

• Make sure you’re running via the Functions host (not dotnet run directly)
  • From the terminal in the function project folder:
    • func start
    • This runs the host and will provide the HostEndpoint.
• Install/update Azure Functions Core Tools
  • Core Tools is what provides the local host runtime.
    • Docs (run local): https://learn.microsoft.com/en-us/azure/azure-functions/functions-run-local
    • Reference: https://learn.microsoft.com/en-us/azure/azure-functions/functions-core-tools-reference
    • GitHub repo: https://github.com/Azure/azure-functions-core-tools
• In Visual Studio: use the Azure Functions debug profile
  • In VS, start the project using the Azure Functions profile (the one that starts the host), not a plain “Project” / console profile.
• Verify your project references include the Worker SDK
  • Missing/incorrect packages can also trigger a broken startup in some setups. Make sure you have:
    • Microsoft.Azure.Functions.Worker
    • Microsoft.Azure.Functions.Worker.Sdk

What not to do

• Don’t try to “fix” it by adding Functions:Worker:HostEndpoint manually to local.settings.json — It’s a host↔worker gRPC endpoint and is normally assigned/passed by the host, not a stable value you set yourself.

In my case, I have reinstalled (fixed the installation) the Azure Functions Core Tools, and after that, restarted Visual Studio, and it solved my problem.

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