AI agents: use the documentation index at llms.txt to locate machine-readable pages. This section is indexed by https://docs.particular.net/nservicebus/llms.txt. The markdown version of this page is served as plain text. An MCP server at /mcp serves the same content via the search_docs and read_doc tools; it is read-only and needs no credentials. Markdown versions of documentation pages are available by appending .md to the page URL. Directory URLs use index.md. They are served as text/plain because some retrieval backends reject text/markdown.

Upgrade Version 1 to 2

Component: Callbacks

Enable callbacks

Callbacks have been made opt-in. In order to make callbacks work they have to be enabled explicitly.

var instanceDiscriminator = ConfigurationManager.AppSettings["InstanceId"];
endpointConfiguration.MakeInstanceUniquelyAddressable(instanceDiscriminator);
endpointConfiguration.EnableCallbacks();

Enabling callbacks in default mode requires the endpoint to be made uniquely addressable.

Enable callbacks without requests

Endpoints only replying to callbacks with object messages like the following:

public class Handler :
    IHandleMessages<Message>
{
    public Task Handle(Message message, IMessageHandlerContext context)
    {
        var responseMessage = new ResponseMessage
        {
            Property = "PropertyValue"
        };
        return context.Reply(responseMessage);
    }
}

don't require a reference to the callbacks package.

For endpoints replying with int or enum results, the callbacks package can be enabled in response-only mode:

endpointConfiguration.EnableCallbacks(makesRequests: false);

In this article