API Visualization with Scalar

Program.cs

using FastEndpoints.Swagger;
using Scalar.AspNetCore; //dotnet add package Scalar.AspNetCore

var bld = WebApplication.CreateBuilder(args);
bld.Services
   .AddFastEndpoints()
   .SwaggerDocument(); //define a swagger doc - v1 by default

var app = bld.Build();
app.UseFastEndpoints(); //must come before the UseOpenApi() call

if (app.Environment.IsDevelopment())
{
    //scalar by default looks for the swagger json file here: 
    app.UseOpenApi(c => c.Path = "/openapi/{documentName}.json");    
    app.MapScalarApiReference();
}

app.Run();

//scalar ui can be accessed at: http://localhost:{port}/scalar/v1

@matthewj-dev
sorry i just saw your question. github didn't send a notification for some reason.
there's no way around having to tell scalar what your "non-default" document name is. but you only need to specify the document name like so:

app.MapScalarApiReference(o => o.AddDocument("my-api-v1"));

visiting /scalar with automatically load up that document since scalar knows about it.
or you'd have to manually visit /scalar/my-api-v1