Add Playground

Adding line 3 using HotChocolate.AspNetCore.Playground and line 45 app.UsePlayground() will add the Playground IDE middle-ware.

./Startup.cs

using HotChocolate;
using HotChocolate.AspNetCore;
using HotChocolate.AspNetCore.Playground;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;


namespace SlackClone
{
    public class Query
    {
        public string Hello => "World";
    }

    public class Startup
    {
        // This method gets called by the runtime. 
        // Use this method to add services to the container.
        // For more information on how to configure your application, 
        // visit https://go.microsoft.com/fwlink/?LinkID=398940
        public void ConfigureServices(IServiceCollection services)
        {
            // Adds GraphQL Schema
            services.AddGraphQL(services =>
                SchemaBuilder.New()
                    .AddServices(services)
                    .AddQueryType<Query>()
                    .Create());
        }

        // This method gets called by the runtime. 
        // Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            // Adds GraphQL Service
            app.UseGraphQL();
            // Adds Playground IDE
            app.UsePlayground();
        }
    }
}

After running the project again by typing dotnet run, visiting localhost:5000/playground should bring up the playground like seen below.