How to add example responses in Swagger in a ASP .NET minimal API?

I would like to add examples of answers for my endpoints in my minimal API in .NET 7.

I have already found several interesting resources but none of them work in the context of a minimal API:

• https://www.dotnetnakama.com/blog/enriched-web-api-documentation-using-swagger-openapi-in-asp-dotnet-core/#api-examples-request-and-response
• https://medium.com/@niteshsinghal85/multiple-request-response-examples-for-swagger-ui-in-asp-net-core-864c0bdc6619

These are the kind of renderings I expect, i.e. a status code, with its description and a specific endpoint (e.g. suppose I have several 400 responses for different cases, I want to be able to differentiate them with a different description and response example).

For example, let imagine that I have the following Startup :

public class Startup
    {
        public IConfiguration Configuration
        {
            get;
        }
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }
        public void ConfigureServices(IServiceCollection services)
        {
            /* ... */
            // Swagger services
            services.AddEndpointsApiExplorer();
            services.AddSwaggerGen(BuilderUtils.SwaggerOptions());             
            /* ... */
        }
        public void Configure(WebApplication app)
        {
            // Swagger activation
            if (app.Environment.IsDevelopment())
            {
                app.UseSwagger();
                app.UseSwaggerUI();
            }

	    /* ... */



            app.MapMyEndpoints();

            app.Run();
        }
    }
}

With the following method:

public static void MapMyEndpoints(this WebApplication app)
{
	app.MapGet("/api/foo", () => return await Foo())
		.WithOpenApi(op => new(op)
		{
			OperationId = "MyOperationId",
			Tags = new List<OpenApiTag> { new() { Name = "MyTag" } },
			Summary = "MySummary",
			Description = "MyDescription"
		});

	app.MapGet("/api/bar", () => return await Bar())
		.WithOpenApi(op => new(op)
		{
			OperationId = "MyOperationId",
			Tags = new List<OpenApiTag> { new() { Name = "MyTag" } },
			Summary = "MySummary",
			Description = "MyDescription"
		});
}

Both will respond using the MessageBody class :

public class MessageBody
{
	public string? Message { get; set; }
        public string? Error { get; set; }
}

For example, Foo will respond either a 200 with the MessageBody :
Message = "Connected",

or 400 with the MessageBody :
Error = "Wrong Password"
or Error = "Account not found"

And it goes on for the other endpoints.

I want to report all of those cases in my Swagger.

Because I work using minimal API, I can't use Exemple Filters, or if I can, I don't know how.

If anyone have a hints on how I can do that I will be really gratefull !

Install the Swashbuckle.AspNetCore.Filters nuget and then you can mark handlers with corresponding attributes:

builder.Services.AddSwaggerGen(options => options.ExampleFilters());
builder.Services.AddSwaggerExamplesFromAssemblies(Assembly.GetEntryAssembly());

// ...

app.MapGet("/api/bar",
        [SwaggerResponseExample((int)HttpStatusCode.OK, typeof(MessageBodyOkExample))]
        [SwaggerResponseExample((int)HttpStatusCode.BadRequest, typeof(MessageBody400Example))]
        () => new MessageBody
        {
            Message = "Connected"
        })
    .WithOpenApi(op => new(op)
    {
        // ...
    })
    .Produces<MessageBody>((int)HttpStatusCode.OK)
    .Produces<MessageBody>((int)HttpStatusCode.BadRequest);

And sample responses:

public class MessageBodyOkExample : IExamplesProvider<MessageBody>
{
    public MessageBody GetExamples()
    {
        return new MessageBody()
        {
            Message = "Connected"
        };
    }
}

public class MessageBody400Example : IExamplesProvider<MessageBody>
{
    public MessageBody GetExamples()
    {
        return new MessageBody()
        {
            Error = "testError"
        };
    }
}

And result: