Here's a compilation of our favorite domain research, monitoring and threat investigation tools and APIs: Domain Research and Threat Investigation: Domain Research and Monitoring Suite, a set of domain research tools that includes Domain monitor, brand monitor, registrant monitor, whois search, reverse whois search, etc All-in-one Domain Research and Monitoring Enterprise API Packages Whoisology.com, the most advanced Reverse Whois tool for finding Deep Connections Between Domain Names & Their Owners TIP, provide threat intelligence APIs and threat intelligence analysis tools with comprehensive information on hosts and the infrastructure behind them Individual domain research tools and APIs: Reverse DNS Lookup, discover all connected domains hosted on the same IP address Bulk Whois API. provides Whois records in bulk for a large number of domain names or IP addresses. Domain Availability API, the most accurate domain availability checker offered Reverse MX Lookup, Reveal all domains that use the same mail server Reverse NS Lookup, Find all domains that use the same name server IP Geolocation API, instantly find an IP address' physical geolocation Reverse Whois, Discover all domain names associated with an individual or an organization. Email Verification API, Email Address Validation Tool to Verify Existence, Validity, & Quality Whois API, provides the registration details, also known as the Whois Record, of a domain name or an IP address. Individual Threat intelligence related tools and APIs: Domain Reputation scoring, Evaluate a domain's reputation based on numerous security data sources as well as on an instant external configuration audit procedure Connected Domains API, Retrieve a list of domain names resolving to a given IP address, including subdomains. Domain Malware check. For a given domain name, check if it is considered to be dangerous in different security data sources. Dangerous domains could be related to a malware distribution network or host a malicious code. SSL Configuration Analysis. For a given domain name, establish and test SSL connection to the host and analyze how it is configured - to detect common configuration issues potentially leading to vulnerabilities. SSL Certificates Chain. For a given domain name, get detailed information about its SSL Certificate and the complete SSL Certificates chain. Domain's Infrastructure Analysis, For a given domain name, get a collection of its web, mail, and name servers as well as its known subdomains. For each infrastructure entry, find out its IP address, geolocation and subnetwork information. Enjoy! This was a sponsored post.