Online tools to check website security?

[LoudLemur]

Sometimes a browser can throw up an error message. It is useful to check what might be the cause and to discover if there are other issues.

Can anybody suggest some online tools which can help with creating a security report?

For example:

https://www.httpcs.com/en/test-ssl-certificate

https://sitecheck.sucuri.net/

[luckow]

https://siwecos.de/en/

[girish]

https://www.ssllabs.com/ssltest/ from Qualys

[DanTheMan]

https://securityheaders.com/

And some information about, who, why and how...
https://securityheaders.com/about/
https://securityheaders.com/faq/