There are few places to get proper analysis of your regular expressions online. One of which is www.regexr.com
My request is simple: Offer a similar service for the regular expression language used in Pi-hole
It is POSIX ERE plus specific extensions (if any): Redirecting...
You are asking for the Pi-hole developers to operate and maintain a web page for testing regex?
Pi-hole specific regex. I have not seen a website that can do the ERE flavor even when it is widely used in Linux (grep).
This does not explain what is what and why. Testing I can also do with simply adding to Pi-hole and check if there are compilation errors. Or using the new test function for regex that is being worked on. The request is more for training and explaining why something is behaving as it is than for checking the outcome.
To be more specific: Something like
There is a difference between seeing what can be done and doing it.
Take (found on reddit)
^(.+[_.-])?(facebook|fb(cdn|sbx)?|tfbnw)\.[^.]+$
or (this too)
^ad([sxv]?[0-9]*|system)[_.-]([^.[:space:]]+\.){1,}|^.+[_.-]ad([sxv]?[0-9]*|system)[_.-]
This is very helpful but it does not support all the things Pi-hole can do (click on the image!):
