Google created the Structured Data Testing Tool (SDTT) which can help you develop, test, and modify your structured markup.
You can load markup into the tool either directly or by supplying a URL. The editing environment for the tool provides these utilities to simplify markup testing:
- Automatic highlighting—once you load your content in the editor, you can click on a validated field on the right of the editor to see which line in your markup produced that field. This is handy for isolating syntax errors.
- Keyword completion of schema.org and JSON-LD keywords.
With Google Structured Data v3 you can directly type in the URL of the part of your page that you'd like to test from within the Dashboard.