Check the HTTP response code for any URL. This is useful for troubleshooting cached redirects and double checking what you're seeing.

A nice and simple tool which checks whether or not the URL/website you enter uses CloudFlare's popular Content Delivery Network (CDN).

Tool to check whether or not a website uses Gzip for compression. Note: This checks the server for the main domain and not third party resources.

A tool written using a WHOis Python wrapper to perform "WHOis" requests which is information related to domain registration.

A DNS Checker which for reasons unknown works pretty damn fast. Find all common DNS entries for any domain which is super handy for site migrations.

In browser check to lookup your computer's IP address, supposed locatio and ISP etc. - useful if you need to be whitelisted.

A fairly niche tool which will visit a website, create a HAR file and convert its JSON format into a more manageable CSV format.