When you're troubleshooting Internet connection problems, one of the first things you'll want to verify is whether the Web site is actually down or if it's just you. If it's you, it could be your Internet provider, your Wi-Fi router, or possibly the device you're connecting from (computer, smartphone, or tablet).
When you're on a desktop computer, you can use something like http://www.downforeveryoneorjustme.com or check the individual status pages from Google, Microsoft, and others. IsDown is an Android app that allows you to quickly check if a Web site is down when you're on your Android device.
To use isDown, type in the URL of the Web site or paste it in from your browser, then tap the light blue "isDown?" button. The white status box will tell you whether or not the site is down. The app also includes the ability to expand shortened URLs, if you want to check the validity or safety of a shortened URL. You can create your own shortened URL as well, via tinyURL.
(Via XDA Developers)