It's easy to accidentally make a formatting mistake or omit a required field when implementing structured data markup. These Google tools will help you find and stamp out problems that could prevent your data from being usable. Test early, test often!
The Structured Data Testing Tool lets you test a single page's markup for correctness. You can either enter a URL for the tool to fetch, or paste in marked-up HTML code directly. Repair all errors reported by the tool before deploying your markup!
The Structured Data Dashboard, a feature of Webmaster Tools, helps you monitor Google's understanding of your structured data over time. To see it, log into Webmaster Tools and click on "Site Appearance," then "Structured Data." You will be able to drill into your data and see Google's understanding of it, including warnings about formatting problems or missing fields.