A route named 'swagger_docs' is already in the route collection. Route names must be unique. Parameter name: name

I have a fresh install of Swashbuckle installed. It ran successfully the first time with one API controller defined and then when I added a second controller, it puked this message.

[ArgumentException: A route named 'swagger_docs' is already in the route collection. Route names must be unique.
Parameter name: name]
   System.Web.Routing.RouteCollection.Add(String name, RouteBase item) +3746353
   System.Web.Http.WebHost.Routing.HostedHttpRouteCollection.Add(String name, IHttpRoute route) +107
   System.Web.Http.HttpRouteCollectionExtensions.MapHttpRoute(HttpRouteCollection routes, String name, String routeTemplate, Object defaults, Object constraints, HttpMessageHandler handler) +357
   Swashbuckle.Application.HttpConfigurationExtensions.EnableSwagger(HttpConfiguration httpConfig, String routeTemplate, Action`1 configure) +440
   Swashbuckle.Application.HttpConfigurationExtensions.EnableSwagger(HttpConfiguration httpConfig, Action`1 configure) +63

[gabrielbarceloscn]

Delete bin/obj folders worked for me.

[archil]

For me the fix was simple. SwaggerConfig contains this line at the start of file

[assembly: PreApplicationStartMethod(typeof(SwaggerConfig), “Register”)]

So it automatically gets called. But I was calling Register method on demand, the old-fashioned way. Removing manual call solved the case