Check whether an IP address is on public spam blocklists. This matters most for mail servers: if their address is listed, many recipients reject the mail.
Your own address is pre-filled, but you can enter any public IPv4 address. The check takes up to four seconds.
Operators of these lists collect IP addresses that sent spam or attacks. Mail servers query the lists for every incoming message and reject mail from listed addresses or file it as spam.
Usually not. Some lists include whole ranges of residential connections because no mail server should send from there. It has no effect on browsing or on sending mail through your provider. It only matters if you run your own mail server.
Spamhaus is the most important list, but only allows automated queries by web services with a dedicated account. Check there directly: check.spamhaus.org