This guide covers the decompilation of VLX files.
Because "VLX" refers to two very different file types depending on the industry, this guide is split into two sections. Skip to the section that matches your needs.
If you are dealing with VLX files (compiled AutoLISP projects), "long story" usually implies you've lost the original source code or are trying to recover a legacy tool. VLX files are "compiled" containers that can include multiple FAS (binary LISP) files, DCL (dialogs), and other resources.
To reverse this, you typically need to follow a multi-step process using specialized (and often old) tools. The VLX Decompilation Workflow
Decompilation is rarely a one-click process. It generally involves two main stages:
Extraction: Pulling the internal .fas files out of the .vlx container. vlx decompiler
Disassembly/Decompilation: Converting those .fas files back into readable .lsp code. Available Tools
According to LispBox, several community-developed tools exist for this purpose:
VLX2FAS Converter: A utility used specifically to convert the .vlx container into its constituent .fas files.
FAS-Disassembler: Converts the binary .fas p-code into a human-readable assembly-like format. Note that this rarely gives you "perfect" source code; you often get variable names like G1234 instead of their original descriptive names.
LSP-Files Decryptor: Used for "protected" .lsp files (older unlisp style), which is different from the modern binary VLX/FAS format. Key Challenges This guide covers the decompilation of VLX files
Version Compatibility: Most decompilers were built for older versions of AutoCAD. If the VLX was compiled with a very recent version of the Visual LISP IDE, these tools might fail or produce garbage output.
Variable Names: High-level metadata like comments and local variable names are usually stripped during compilation. You will likely spend a "long story" worth of time renaming variables to make the code maintainable again.
Legal/Ethical Note: Ensure you have the right to decompile the software. This is typically done for source recovery when the original developer is unavailable or files were lost.
If you are looking for these specific utilities, they are often hosted on niche CAD forums or archival blogs like LispBox.
If you have a specific error or a certain version of AutoCAD you're targeting, please let me know: Which AutoCAD version was used to compile the file? Summary Checklist
Are you trying to recover your own lost code or analyze a third-party tool? What operating system are you running the tools on?
In rare cases, VLX refers to an older Visual Basic or Delphi library format used by the QSoft framework.
findstr on the VLX binaryOpen the VLX in a hex editor. Search for (defun. Because compilation does not fully encrypt the string table, you can often see the original function names and literal strings (like prompts, error messages) intact.
A VLX (Visual LISP eXecutable) file is a compiled, binary format used by AutoCAD and its derivatives (like BricsCAD, IntelliCAD). It is generated by the Visual LISP compiler from one or more source files (.lsp, .fas, .dcl).
Key characteristics:
.lsp..vlxDecompiling VLX files is often a violation of the software's Terms of Service. Only decompile files you own or have explicit permission to reverse engineer.
Use the VL-COMMENT or check the VLX's digital signature. Many developers forget to strip metadata. Tools like strings (Sysinternals) can extract text snippets from the VLX, including email addresses or website URLs.