Many tools claiming to be a "Facebook Profile Viewer No Account" are
Most websites or apps claiming to be a "Facebook Profile Viewer" that require no account are malicious scams www.thestreet.com They Cannot Bypass Privacy
: Facebook's security architecture ensures that if a profile is set to "Private" or "Friends Only," the data is literally not served to the web browser or API without a valid, authorized login. Hidden Dangers
The long answer is more nuanced, but the bottom line is this:
: Before "results" are shown, the user is forced to complete surveys, download software, or provide personal email addresses.