Boarding pass barcodes may contain personal data, including full name, record locator, and frequent flier number. With this information, someone could change or cancel your flights. Be sure you trust any scanner or website you provide your barcodes to, and avoid providing barcodes to anybody until your entire itinerary is complete.
This website parses boarding passes locally in your browser, and does not send the data to the server. However, if you use the share link, the boarding pass data will be embedded in the share link. Anyone you share it with may have access to the data, and it’s possible that this website’s host may have access to these share links from its logs.