Or an alternative open source one that you can self-host is https://github.com/gskinner/regexr https://github.com/gskinner/regexr and https://regexr.com/ https:

Or an alternative open source one that you can self-host is https://github.com/gskinner/regexr https://github.com/gskinner/regexr and https://regexr.com/ https://regexr.com/