Update README.md

README.md

@@ -134,17 +134,17 @@ A list of search engines useful during Penetration testing, vulnerability assess
 
 
 ### DNS
-- [DNSDumpster](https://dnsdumpster.com/)
-- [RapidDNS](https://rapiddns.io/)
-- [DNSdb](https://docs.farsightsecurity.com/#dnsdb)
+- [DNSDumpster](https://dnsdumpster.com/) - dns recon & research, find & lookup dns records
+- [RapidDNS](https://rapiddns.io/) - dns query tool which make querying subdomains or sites of a same ip easy
+- [DNSdb](https://docs.farsightsecurity.com/#dnsdb) - Passive DNS historical database
 - [Omnisint](https://omnisint.io/reverse-dns-lookup) - Reverse DNS lookup
-- [HackerTarget](https://hackertarget.com/ip-tools/)
-- [passivedns.mnemonic.no](https://passivedns.mnemonic.no/)
-- [ptrarchive.com](http://ptrarchive.com/)
-- [dnshistory.org](http://dnshistory.org/)
-- [DNSTwister](https://dnstwister.report/)
-- [DNSviz](https://dnsviz.net/)
-- [C99.nl](https://api.c99.nl/)
+- [HackerTarget](https://hackertarget.com/ip-tools/) - Collect information about IP Addresses, Networks, Web Pages and DNS records
+- [passivedns.mnemonic.no](https://passivedns.mnemonic.no/) - Web interface for querying passive DNS data collected in our malware lab
+- [ptrarchive.com](http://ptrarchive.com/) - Over 230 billion reverse DNS entries from 2008 to the present
+- [dnshistory.org](http://dnshistory.org/) - Domain Name System Historical Record Archive
+- [DNSTwister](https://dnstwister.report/) - The anti-phishing domain name search engine and DNS monitoring service
+- [DNSviz](https://dnsviz.net/) - Tool for visualizing the status of a DNS zone
+- [C99.nl](https://api.c99.nl/) - Over 57 quality API's and growing
 
 
 ### Certificates