Fetch as Google is a handy feature of Google Webmaster Tools that allows you to simulate how Google crawls or renders a URL on your site, then gives you the option to submit that URL to the index.
Fetch as Google has different Googlebot types you can choose from, including Desktop and Mobile: Smartphone. Once you’ve chosen your Googlebot, you can then “Fetch and Render” the URL, which will give you details on the URL’s HTTP response, the page download speed, and how Google sees your page (vs. how browsers see it).
This is a great (and quick) tool to use to detect basic errors (e.g. whether your URL being redirected or blocked by robots.txt) and also to see the response time of your server.