builder.Services.AddHttpClient<...>() doesnt work with the class marked as [McpServerToolType] directly

[RodgeFu]

Describe the bug
I have created a simple McpServerTool class whose ctor takes a HttpClient as parameter like below:

    [McpServerToolType]
    public sealed class PetsService
    {
        private readonly HttpClient _httpClient;

        public PetsService(HttpClient httpClient)
        {
            _httpClient= httpClient;
        }

        [McpServerTool]
        [Description("List all pets")]
        public async Task<Page_Pets> ListPetsAsync(
            int? limit, string? continuationToken, CancellationToken cancellationToken = default
        )
        {...}
    }

Then in the Program.cs, I want to inject the HttpClient like below, but it seems not work:

            builder.Services.AddHttpClient<PetsService>(client =>
            {
                client.BaseAddress = new Uri("https://localhost:7387/pets");
            });

And when I am trying things around, I found if I create a wrapper class of HttpClient (i.e. HttpClientWrapper whose ctor takes HttpClient) and use that as the parameter of my McpServerTool class's ctor, then adding builder.Services.AddHttpClient<HttpClientWrapper>(...), the injection can work properly when the HttpClientWrapper is instantiated.

So is it supported to inject HttpClient against the class marked as "McpServerToolType" directly? Or did I do it in a wrong way? thanks.

Expected behavior
AddHttpClient<...>(...) can work with the class marked as "McpServerToolType" directly.

[halter73]

Thanks for filing this issue.

So is it supported to inject HttpClient against the class marked as "McpServerToolType" directly? Or did I do it in a wrong way? thanks.

This is not supported. Registering an MCP handler type as a typed client does not align with the intended usage of typed clients which is to act as an HttpClient wrapper that gets injected into your app.

So, in the case of your PetsService example, the PetsService should be the thing that gets injected into your [McpServerToolType] rather than the tool type itself.

Typed clients:

• Provide the same capabilities as named clients without the need to use strings as keys.
• Provide IntelliSense and compiler help when consuming clients.
• Provide a single location to configure and interact with a particular HttpClient. For example, a single typed client might be used:
  • For a single backend endpoint.
  • To encapsulate all logic dealing with the endpoint.
• Work with DI and can be injected where required in the app.

https://learn.microsoft.com/dotnet/core/extensions/httpclient-factory#typed-clients

If you don't want to define an extra type, you can use a named client instead.

[KeyurRamoliya]

@RodgeFu As per the @halter73 comment you can do it like this using named clients. The same logic you will also find in ProtectedMcpServer service for WeatherApi.

Register a named HttpClient

builder.Services.AddHttpClient("PetsApi", client =>
{
	client.BaseAddress = new Uri("https://localhost:7387/pets");
	// Add any other configuration like headers, timeout, etc.
});

Update your MCP tool to use IHttpClientFactory

[McpServerToolType]
public sealed class PetsService
{
	private readonly IHttpClientFactory _httpClientFactory;

	public PetsService(IHttpClientFactory httpClientFactory)
	{
		_httpClientFactory = httpClientFactory;
	}

	[McpServerTool]
	[Description("List all pets")]
	public async Task<Page_Pets> ListPetsAsync(int? limit, string? continuationToken, CancellationToken cancellationToken = default)
	{
		using var httpClient = _httpClientFactory.CreateClient("PetsApi");
		var response = await httpClient.GetAsync($"/pets?limit={limit}&token={continuationToken}", cancellationToken);
		// Parse and return Page_Pets
		return parsedResult;
	}
}