Link validation checks that all your links are working and going to the right pages. Access the Link Validator by clicking the Links button in the bottom right corner. Parcel will attempt to connect to each link you have in your HTML and tell you if the connection is secure/successful. If the button says In Sync, then the validation results match the code. If you make code changes, the button will change to Refresh. Click Refresh to run the validator check again.
Clicking on any link in the validator will open that link in a new tab. Multiple identical instances of the same link will only show up once in the results.