What Are the .NET Platform File Extensions?

Probably the easiest place to look is the master web.config file, which is where base settings for ASP.NET are declared. This includes <httpHandlers>, e.g.:

<httpHandlers>  <add verb="*" path="*.rules" type="System.Web.HttpForbiddenHandler" validate="true"/>  <add verb="*" path="*.xoml" type="System.ServiceModel.Activation.HttpHandler, System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" validate="false"/>  <add path="*.svc" verb="*" type="System.ServiceModel.Activation.HttpHandler, System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" validate="false"/>  <add path="trace.axd" verb="*" type="System.Web.Handlers.TraceHandler" validate="True"/>  <add path="WebResource.axd" verb="GET" type="System.Web.Handlers.AssemblyResourceLoader" validate="True"/>  <add path="*.axd" verb="*" type="System.Web.HttpNotFoundHandler" validate="True"/>  <add path="*.aspx" verb="*" type="System.Web.UI.PageHandlerFactory" validate="True"/>  <add path="*.ashx" verb="*" type="System.Web.UI.SimpleHandlerFactory" validate="True"/>  <add path="*.asmx" verb="*" type="System.Web.Services.Protocols.WebServiceHandlerFactory, System.Web.Services, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" validate="False"/>  <add path="*.rem" verb="*" type="System.Runtime.Remoting.Channels.Http.HttpRemotingHandlerFactory, System.Runtime.Remoting, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" validate="False"/>  <add path="*.soap" verb="*" type="System.Runtime.Remoting.Channels.Http.HttpRemotingHandlerFactory, System.Runtime.Remoting, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" validate="False"/>  <add path="*.asax" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.ascx" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.master" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.skin" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.browser" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.sitemap" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.dll.config" verb="GET,HEAD" type="System.Web.StaticFileHandler" validate="True"/>  <add path="*.exe.config" verb="GET,HEAD" type="System.Web.StaticFileHandler" validate="True"/>  <add path="*.config" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.cs" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.csproj" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.vb" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.vbproj" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.webinfo" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.licx" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.resx" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.resources" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.mdb" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.vjsproj" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.java" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.jsl" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.ldb" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.ad" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.dd" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.ldd" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.sd" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.cd" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.adprototype" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.lddprototype" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.sdm" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.sdmDocument" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.mdf" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.ldf" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.exclude" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*.refresh" verb="*" type="System.Web.HttpForbiddenHandler" validate="True"/>  <add path="*" verb="GET,HEAD,POST" type="System.Web.DefaultHttpHandler" validate="True"/>  <add path="*" verb="*" type="System.Web.HttpMethodNotAllowedHandler" validate="True"/></httpHandlers>