The windows iRule Editor has had a very long life. But...it hasn't been updated in years and really should be sunsetted in your environment. There have been other attempts along the way, from a personal project with a Mac desktop app written in python and Qt that never made it past me, an Eclipse plugin several years back that gained a little traction, but the iRule Editor Joe Pruitt created lived on through all of that.
However, there are a couple fantastic options now in the Visual Studio Code marketplace that combine to make for a great iRules development environment and also include the ability to pursue the automation toolchain development as well. Here are the tools you'll need: