A better decompiler does not guess the compilation standard. It reads the VLX header signature, identifies the version of the Visual LISP engine used (e.g., 16.x vs 20.x), and swaps in the correct parser tree. This version-aware architecture means a VLX created in AutoCAD 2020 decompiles as cleanly as one from AutoCAD 2008.

The better tool uses . It looks at the distance between the definition of V1002 and its use in a princ statement. It realizes that V1002 is multiplied by another variable that is fed into a getdist function. Hence, V1002 becomes distance_input . No AI magic—just clever statistical mapping.

Historically, FAS files were simple to read. However, Autodesk introduced encryption/obfuscation in newer versions (AutoCAD 2013+). The bytecode stream is often XOR-chained or bit-shifted. This is where "better" decompilation happens.

The Fas-Disassembler/Decompiler (Fas-Dis) is the primary open-source effort to make .VLX and .FAS decompilation "better" through constant updates.

Fas-Disassembler/Decompiler for AutoCAD Visual Lisp · GitHub