Https://leakcheck.io/ - Payed, But you get passwords in clear text and there's a cheap 1 time payment option! Source: about 1 year ago

Sharing is caring, so I'll share one of mines. I tend to use google dorking as usual, but also use LeakCheck which is a rather handy tool to receive clear text passwords from Usernames, Email Addresses and such. Are there any other places, like these, that can be of use? :). Source: about 1 year ago

You could try https://leakcheck.net/ or https://www.dehashed.com/ (personally best for me) but they are paid unfortunately. Source: over 2 years ago

There was a data breach last year. Check on https://leakcheck.net/ whether your details were on there. Source: over 2 years ago

I think https://leakcheck.net/ might be the one you're looking for. For personal emails I use hacknotice.com. Source: about 3 years ago

BUT - As far as resources for building out the regex patterns, I use regexpal.com and a copy of this https://cheatography.com/davechild/cheat-sheets/regular-expressions/pdf/ printed out beside me. Once you get into it, the power of subgroups, and lookahead/behind processing beats some of the mental gymnastics you would need to go to code it out in your language of choice. Source: almost 2 years ago

Spend an afternoon really diving into it, bookmark regexpal.com, and call it a day IMO. Source: about 2 years ago

i’m a professional developer and I just relearn it every time I need it, which is about once or twice a year, but depending on someone’s specialty they may swim around in it all day. It can get really complicated. https://regexpal.com is where I kick it around testing until it works. Source: about 2 years ago