The tool is called: Facebook Debugger. It is simple to use and forces Facebook to re-index or re-scrape updated information from a URL.
1. Go to https://developers.facebook.com/tools/debug/. You must be logged in to a Facebook account to use the tool.
2. Paste in the URL you wish to have Facebook re-scrape and click "Debug".
3. The debugger will show all the existing "scrape" information Facebook has for that URL. To force Facebook to re-scrape the URL and pull in new information, click "Fetch New Scrape Information".
4. After new information is scraped, scroll down to the bottom of the page. Under the heading " When Shared..." you will see what your URL will look like when shared or posted to Facebook.