The validation feature shows you which records would be deployed if actually deploying the data set. Because no destination org is involved, the validation results do not show potential deployment errors or which record handling operation (insert, update, upsert) would be used for each record. 

To validate a data set deployment from the data set editor:

1. From the Data Set Editor, click Simulate.
2. Here you will be directed to the Deploy page to select your source and destination.
3. The data set should be preselected.
4. Click Validate at the bottom of the page.
5. You will be directed to the Deployment History page where your Validation will appear at the top of the list.
6. Select the deployment to open the Deployment Results page.
7. Monitor the progress of the validation on the Deployment Results page.
8. Monitor the validation activity in real-time on the Activity section of the page.

6. On the Deployment Results page, the results will appear below the activity.