DomainTools is described as 'Domain name research, including comprehensive Whois Lookup, Reverse Whois Lookup and Whois History. Domain name monitoring tools and buyer/seller tools'. There are more than 25 alternatives to DomainTools, not only websites but also apps for a variety of platforms, including Self-Hosted solutions, Windows, Linux and SaaS. The best alternative is ViewDNS.info. It's not free, so if you're looking for a free alternative, you could try JsonWhois.io or DomainMOD. Other great sites and apps similar to DomainTools are WebCargo (Paid), Robtex Swiss Army Knife Internet Tool (Free), WhoisAPI (Freemium) and CubDomain (Free).
JsonWhois is the leading cloud hosted Whois API. The service serves WHOIS records for domains and IP addresses through a fully RESTful API. Additionally, the service offers IP geolocation and URL to screenshot services. Free usage per month!.
WhoisAPI is the premier provider of freshly parsed whois data for domain names and IP addresses, also providing IP to geolocation, HTML to PDF, and domain availability RESTful HTTP APIs. Billing is performed on a pay as you go basis, free monthly use.
Online-Domain-Tools.com makes your online life easier and happier. Various domain tools, network tools, web and browser tools, security and privacy tools, data and conversion tools, and coders tools are ready to be used immediately.