Domain and IP APIs serve various functions, such as domain search and availability, IP/domain lookup, and providing customer insights. Among the top APIs identified are FullContact Enrich API, which enriches data fragments into comprehensive customer profiles, and Domainr API, which offers domain search and status checking. Whois API facilitates domain name lookups in XML or JSON formats, while Telize API provides IP and GeoIP information. Sqreen API assesses security risks associated with IPs and emails. StatDNS API allows for DNS queries and reverse PTR records, IP Info API offers IP location insights, and BigData Cloud's IP Geolocation API provides precise geolocation data for IPv4 addresses. Each API offers various pricing models, with some providing free tiers and others requiring payment for extended use.