There is a wealth of online security scanners available. Many of them are trial offers to get you to sign up for a paid subscription of their service.
Below some of my favorite scanners that don't require you to sign-up:
Observatory by Mozilla (https://observatory.mozilla.org/)
Observatory is a simple tool that allows site operators to quickly assess not just if they are using these technologies, but also helps them identify how well they’re being used. It uses a simple grading system to provide near instant feedback on site improvements as they are made. To assist developers and administrators, Observatory also provides links to quality documentation that demonstrates how these technologies work.
SSL Labs Server Test (https://www.ssllabs.com/ssltest/)
This free online service from Qualys performs a deep analysis of the configuration of any SSL web server on the public Internet.
SSL Labs Browser Test (https://www.ssllabs.com/ssltest/viewMyClient.html)
This tool checks your browsers SSL implementation looking at protocol support and different vulnerabilities.
HTTP/2 Test (https://tools.keycdn.com/http2-test)
HTTP/2 Test allows you to verify whether your server provides HTTP/2.0 Support. Although HTTP/2.0 doesn't directly provide better security it might give you a bigger incentive to use SSL since it will improve your website performance significantly.
MxToolBox SuperTool (https://mxtoolbox.com/SuperTool.aspx)
All of your MX record, DNS, blacklist and SMTP diagnostics in one integrated tool.
WHOIS IP Lookup Tool (https://www.ultratools.com/tools/ipWhoisLookup)
The IPWHOIS Lookup tool finds contact information for the owner of a specified IP address.
GeoIP2 Precision service (https://www.maxmind.com/en/home)
The IPWHOIS Lookup tool also finds contact information for the owner of a specified IP address as well as where which country the IP might be located.
OpenDNS Cache Check (https://cachecheck.opendns.com)
A domain might may point to different IPs around the world. The cache check from OpenDNS is a very quick way to find out what IPs a domain might resolve to from different locations.