diff --git a/README.md b/README.md
index 34e73757a..12ef14787 100644
--- a/README.md
+++ b/README.md
@@ -13,10 +13,13 @@ Testing
 ------------------------------------------------------------------------
 
 You can make and test client changes simply by opening `testclient.html`.
-
 This will allow you to test changes to the client without setting up your
 own login server.
 
+You can connect to an arbitrary server by navigating to
+`testclient.html?~~host:port`. For example, to connect to a server running
+locally on port 8000, you can navigate to `testclient.html?~~localhost:8000`.
+
 Certain things will fail:
 
 + Registering
diff --git a/testclient.html b/testclient.html
index a97603946..b2519fdba 100644
--- a/testclient.html
+++ b/testclient.html
@@ -19,6 +19,20 @@
 			serverprotocol: 'ws',
 			testclient: true
 		};
+		(function() {
+			if (location.search !== '') {
+				var m = /\?~~(([^:\/]*)(:[0-9]*)?)/.exec(location.search);
+				if (m) {
+					Config.serverid = m[1];
+					Config.server = m[2];
+					if (m[3]) {
+						Config.serverport = m[3];
+					}
+				} else {
+					alert('Unrecognised query string syntax: ' + location.search);
+				}
+			}
+		})();
 	</script>
 	<!--[if lte IE 8]><script>
 		oldie = true;