diff --git a/application.go b/application.go
index b8f9322..a7367b0 100644
--- a/application.go
+++ b/application.go
@@ -3,6 +3,7 @@ package nasin
 import "log"
 import "image"
 import "strings"
+import "net/url"
 import "git.tebibyte.media/tomo/tomo"
 import "git.tebibyte.media/tomo/nasin/internal/registrar"
 
@@ -15,6 +16,20 @@ type Application interface {
 	Init () error
 }
 
+// ApplicationURLOpener is an application that can open a URL.
+type ApplicationURLOpener interface {
+	Application
+
+	// OpenURL opens a new window with the contents of the given URL. If the
+	// given URL is unsupported, it returns an error (for example, an image
+	// viewer is not expected to open a text file). If the URL scheme is
+	// empty, file:// is assumed.
+	//
+	// Applications should support the file:// scheme at the very least, and
+	// should also support others like http:// and https:// if possible.
+	OpenURL (*url.URL) error
+}
+
 // ApplicationDescription describes the name and type of an application.
 type ApplicationDescription struct {
 	// The name of the application.