How to Load a LISP Routine in AutoCAD
To load a LISP routine in AutoCAD, type APPLOAD at the command line, browse to your .lsp, .fas, or .vlx file, and click Load. The routine is available immediately for the current session. To load it every time AutoCAD starts, click Contents under Startup Suite in the same dialog and add the file there.
Steps
Open the Load/Unload Applications dialog
Type APPLOAD at the command line and press Enter. The Load/Unload Applications dialog opens.
Browse to your LISP file
Use the file browser to locate your .lsp, .fas, or .vlx file. Set the file type filter to AutoCAD Apps (*.arx; *.crx; *.lsp; *.dvb; *.dbx; *.vlx; *.fas) if needed.
Load the file
Select the file and click Load. AutoCAD shows 'Successfully loaded.' at the bottom of the dialog. If you get a security warning, the folder isn't in Trusted Locations — click 'Always Load' or add the folder under Options → Files → Trusted Locations.
Run the new command
Close the dialog. Type the command name the routine added (usually documented by the seller, e.g. CADEXTOOL) and press Enter. If you don't know the command name, look inside the .lsp for (defun C:NAME …) — NAME is the command.
Add to Startup Suite (optional)
Open APPLOAD again. In the Startup Suite section, click Contents, then Add, browse to the file, and click Open. Close. The routine now loads automatically every AutoCAD session.
Frequently asked questions
Why doesn't AutoCAD recognize my command after loading?
Check the spelling of the command in the source .lsp — look for (defun C:NAME …). The C: prefix makes it a command; without it the function is callable only from other LISP code.
I get a security warning every time I load. How do I stop it?
Add the folder containing the LISP file to Options → Files → Trusted Locations. AutoCAD will load files from trusted folders without warning. Never blanket-disable SECURELOAD — it's there to stop malicious LISP.
What's the difference between APPLOAD and (load "file.lsp")?
APPLOAD is the GUI; (load "file") is the command-line equivalent typed into AutoCAD. Both do the same thing. (load) is useful inside ACAD.lsp/acaddoc.lsp for chaining loads.
Can I load a .fas the same way as a .lsp?
Yes. APPLOAD, (load), and the Startup Suite all handle .lsp, .fas, and .vlx identically. Compiled .fas/.vlx just load faster and hide the source code.
Will the routine survive an AutoCAD restart?
Only if you added it to the Startup Suite or referenced it from ACAD.lsp/acaddoc.lsp. A plain APPLOAD is session-scoped — close AutoCAD and it's gone.
Related guides
Four ways to make a LISP routine load automatically — Startup Suite, ACAD.lsp, acaddoc.lsp, and Trusted Locations — and which to pick.
Load a C# / VB.NET plugin DLL into AutoCAD with NETLOAD, troubleshoot common load errors, and set up auto-load so you don't NETLOAD every session.
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Related terms
A scripting language used to automate AutoCAD by writing routines that issue commands, query drawings, and build custom tools.
Autodesk's dialect of LISP, built into AutoCAD since 1986, used to write custom commands and automate drawings.
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.
The AutoCAD command that opens a dialog for loading .lsp, .fas, .vlx, .arx, or .dll files into the current session.
AutoCAD's allow-list of folders that can load executable code (LISP, .NET, ARX) without a security warning.