The fundamental AppleScript file format is the compiled script file. It consists of bytecode, not the original text. It also can maintain other information, such as the persistent values of top-level entities (mostly properties, globals, and script objects) and certain context information. A compiled script file can be executed directly, with very little delay (because there is no need to compile). Many environments that can run scripts expect a compiled script file.

When you run a compiled script in Script Debugger and then save (without editing further), values of top-level entities are saved as well.

The life of the AppleScript programmer is made more complicated by the fact that compiled script files now come in a variety of formats. Not all of these are compatible with every system or every script-editing or script-running environment.

Also, a compiled script can have difficulty opening if a required application or scripting addition is missing. If the script was saved with Script Debugger, you may still be able to open the script as text.