AGIWiki/Logic editor
Nowadays AGI developer should have no trouble finding suitable logic editor, as AGI IDEs such as AGIWiki/AGI Studio, WinAGI and QT AGI Studio each provide own, internal editor. However, in the 1990s available logic editors were mostly separate MS-DOS-applications with exception of Alex Simkin's AGDS, which, regardless attempting being a commercial product, was the first fanmade AGI IDE, though in Russian and using own encryption string, incompatible with Sierra's games. In 1997 Peter Kelly released AGI Studio's first version. Helen Zommer wrote Linux alternative Linux AGI Studio which was ported to Windows by Nat Budin in 2001 as Windows Linux AGI Studio. Linux AGI Studio is currently known as QT AGI Studio.
While almost all of those environments can and will save their sources to external files with possible documentation editable with any texteditor, most environments provide useful features such as syntax highlighting, running compiler and debugging.