As you connect to your data, the preview window enables you to peek at your data, to ensure it's what you're looking for, before you create and save the data source.
Here's an example of the preview window:
To get you to your data faster, this preview only includes up to 2MB of data. This might lead you to believe that Klipfolio isn't getting all of the data you requested, especially for data sources that return a LOT of data. No worries! After creating the data source, simply navigate to the About this Data Source page to see a preview that includes ALL of the data you requested. (To access the About this Data Source page, click Data Sources in the left navigation sidebar and select the desired data source.)