https://mxtoolbox.com/SuperTool.aspx - DNS, A, MX, NS etc etc checker
https://dnsmap.io/#A/ - dns propagácia
https://www.iplocation.net/ - IP location
https://apps.db.ripe.net/db-web-ui/#/query
https://www.sslshopper.com/ssl-checker.html#hostname= - SSL checker
https://www.diffnow.com/report - porovnávač kódu dvoch súborov / url
https://tinyjpg.com/ - jpg/png compressor
https://md5file.com/calculator - MD5 calculator - from files
https://hash.online-convert.com/md5-generator - MD5 calculator from files + url
https://www.checktls.com/TestReceiver - mail tester
https://www.sslshopper.com/ssl-checker.html - SSL checker
https://www.ssllabs.com/ssltest/index.html - SSL grade tester
https://chceck-your-website.server-daten.de - DNSSEC troubleshooting
https://www.holylinux.net/content/bash-script-check-ssl-certificates-expiration
https://decoder.link/sslchecker/
https://httpstatus.io/