How to Compile a LISP Routine to FAS
To compile a LISP routine to FAS: in AutoCAD, type VLIDE, open your .lsp in the Visual LISP IDE, then File → Make Application → New Application Wizard, pick 'Simple' for single-file FAS, follow the prompts. Visual LISP produces a .fas next to your .lsp that loads identically but ships without source code.
Steps
Open Visual LISP
In AutoCAD, type VLIDE (or VLISP). The Visual LISP IDE opens in a separate window.
Open your .lsp file
File → Open File → browse to your .lsp source. The file opens in an editor tab with syntax highlighting.
Launch the Application Wizard
File → Make Application → New Application Wizard. Pick 'Simple' for a single .lsp file → .fas. Pick 'Module' if you have multiple .lsp files to bundle into one .vlx.
Choose Simple → next
Set the Application Location (where to write the .fas) and the Application Name. Add your .lsp file. Step through Next → Next → Finish.
Build
In the resulting Project window, click 'Make' (the hammer icon). Visual LISP compiles your source into a .fas next to it. The output window shows any errors.
Distribute
Ship the .fas alone. Buyers load it the same way they would the original .lsp — APPLOAD or Startup Suite. Source is hidden.
Frequently asked questions
Does compiling to FAS hide my source code completely?
It hides the original text. .fas is bytecode, not encryption — a determined attacker can decompile it. For real source protection, write the value-critical logic in .NET and ship a signed/obfuscated DLL.
What's the difference between FAS and VLX?
.fas is one compiled file. .vlx is a single packaged bundle of multiple .fas files plus optional resources (DCL dialogs, support data). Use FAS for single-file utilities; use VLX for larger apps.
Will the FAS work in any AutoCAD version?
Yes — FAS is forward and largely backward compatible across AutoCAD versions. The exception is FAS that uses LISP functions only added in newer AutoCAD releases — those won't work in older versions.
Can I edit a .fas?
No. .fas is compiled. Keep the original .lsp source under version control — that's the editable form.
Related guides
Three reliable ways to load .lsp, .fas, and .vlx files into AutoCAD, plus how to add them to the Startup Suite so you never reload again.
Write, save, and load a five-line LISP routine that adds a custom command to AutoCAD.
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Related terms
A compiled, single-file binary of an AutoLISP/Visual LISP routine. Faster to load and obscures the source code.
A compiled Visual LISP application that bundles multiple .lsp/.fas files, DCL dialogs, and resources into one file.
An extended LISP environment in AutoCAD that adds an IDE, debugger, COM access, and the ability to compile to FAS or VLX.
Autodesk's dialect of LISP, built into AutoCAD since 1986, used to write custom commands and automate drawings.