I get HTTP error 400 every time I try to access url without the trailing slash from Java. This code works fine without proxy or when using other proxy software (I'm using Windows 10 and latest Java 8) so I suspect it's a Fiddler bug. System.setProperty("java.net.useSystemProxies", "true"); URL res = new URL("http://en.wikipedia.org"); HttpURLConnection request = (HttpURLConnection) res.openConnection(); request.connect(); request.getDoOutput(); System.out.println(request.getResponseCode());