This is a regular expression checker especially programmed for rsyslog. Rsyslog uses POSIX ERE (and optionally BRE) expressions. This checker works with the php POSIX ERE functions. So in theory, there can be a difference between what the engine included in rsyslog (clib) and this web app does. However, in practice the results should be fairly the same. Note: you need at least rsyslog version 3.19
![Regex - rsyslog](https://cdn-ak-scissors.b.st-hatena.com/image/square/2bddaa826b5c95ab231a5eabe3c2224b9d855767/height=288;version=1;width=512/https%3A%2F%2Fwww.rsyslog.com%2Ffiles%2F2018%2F02%2Frsyslog-logo-512x512.png)