The purpose of origin.tlscheck.xyz is to set some cookies and see the effect of the SameSite cookie attribute - and recent changes in browser behavior.
The test involves 3 sites, one origin site setting the cookies, an other site in the same registrable domain, and a site in a different registrable domain
To get started, click this link to set some cookies from the origin site https://origin.tlscheck.xyz/cgi-bin/ss-set-cookie.