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All about JSFX Plugins

What are JSFX?

JSFX are free, open-source audio plugins.

In their most simple form, JSFX are text files that create plugins for Cockos Reaper DAW.

A Dynamic Text-Mode Live FX processor!

When placed in REAPER’s Effects folder, they become fully fledged plugins available to use in Reaper under the ‘JS’ category in much the same way as VST plugins. However, unlike VST plaugins, they are editable from within Reaper and and changes made to the plugin’s code are updated live.

JSFX are written the EEL2 programming language, developed by Cuckos. They have nothing to do with JavaScript. (Despite the fact that JavaScript can also be used for audio processing, neither Reaper nor JSFX contain or make use of any JavaScript).

The JS in JSFX is short for Jesusonic, which is sometimes used to describe the programming language itself, but is actually related to an earlier implementations of what is now known as EEL2. EEL2 gets its name from EEL - Extensible Embeddable Language, which was developed around 2002 and specifically aimed at scripting in realtime systems (such as audio). However, EEL and EEL2 should not be confused and scripts written in EEL will not work for JSFX. The origins and etymology of the name Jesusonic are known only to its creator, Justin Frankel. However, it’s safe to say Jesus (as in Christ) has very little to do with it!

JSFX are simply text files requiring no extension to run, but are often given the extension .jsfx to differentiate them from other files.

Reaper comes bundled with a variety of pre-installed JSFX plugins, which are categorized under ‘JS’ within Reaper’s FX section.

Reaper includes its own IDE for scripting which enables any of the built-in JSFX to be inspected or modified, as well as giving the user the ability to create their own JSFX plugins using the EEL2 scripting language.

However, it is not mandatory for the Reaper IDE to be used, JSFX can be created simply in a text editor or in any other IDE such as VSCode or X-code. In order for a JSFX plugin to load in Reaper, the relevant code file simply has to be placed in the correct user folder, on Windows this is usually

"C:/Users/<<USERNAME>>/AppData/Roaming/
REAPER/Effects"