DCV Inspector helps you inspect the DNS, HTTP, and SMTP requests made by a certificate authority during domain control validation (DCV). You can use it to detect violations of domain validation rules, such as the use of Delegated Third Parties.
DCV Inspector creates a unique subdomain for each test. All DNS queries, HTTP requests, and emails to this subdomain (including descendants of the subdomain) are recorded and presented to you for inspection.
Hardenize is a domain hardening checker that covers various aspects. It checks for the presence of basic security extensions and protocols for DNS, email, and web content. This covers such aspects as DNSSEC and CAA records for DNS, email encryption and security like SPF, DMARC, and DANE, and for the web valid certificates and security headers like HSTS or CSP.
https://developer.mozilla.org/en-US/observatory
Certificate | HTTP | TLS | ToolWebsite quality measurement tool. The website measures the quality of HTTP headers which improve security. Additionally, it provides inspections for the TLS certificate and SSH servers. It also includes many third-party tools.
The HTTP standard is quite complex and is specified in multiple IETF RFC documents.
Scan a website for the HTTP headers returned and how good the security related headers are.
https://github.com/aaronpowell/httpstatus
HTTP | ToolThis is a super simple service for generating different HTTP codes. It's useful for testing how your own scripts deal with varying responses. Just add the status code you want to the URL, like this: https://httpstat.us/200
The service allows many status codes, can add delays to the response, or return random ones. This can be useful for testing tools or code.