How to Write Your First AutoLISP Routine
To write your first AutoLISP routine, open Notepad, paste (defun C:HELLO () (princ "Hello CAD")(princ)), save as hello.lsp, then APPLOAD it in AutoCAD and type HELLO. That five-line file is a complete, working LISP routine.
Steps
Open a text editor
Notepad, Notepad++, or VS Code (with the AutoCAD AutoLISP extension) all work. Avoid Word — it injects formatting that breaks AutoLISP parsing.
Write the routine
Paste: (defun C:HELLO ( / ) (princ "\nHello from your first LISP routine!") (princ) ) The C: makes HELLO a command. The ( / ) declares no arguments and no local variables. (princ) at the end suppresses nil output.
Save the file
Save As → choose 'All Files' so the .txt extension isn't appended. Name it hello.lsp and save somewhere on your AutoCAD support path (or any trusted folder).
Load the file
In AutoCAD, type APPLOAD. Browse to hello.lsp. Click Load. The command line says 'Successfully loaded.'
Run your command
Type HELLO at the command line and press Enter. You should see your message print.
Extend it
Try replacing the body with (command "_LINE" "0,0" "10,10" "") to draw a line, or (entget (car (entsel))) to print the DXF data for any entity you click. The AutoLISP Reference (F1 → Developer Documentation) lists every function.
Frequently asked questions
AutoCAD says 'Unknown command HELLO'. What did I do wrong?
Three things to check: (1) the file actually loaded — APPLOAD → Loaded Applications; (2) the function is defined as C:HELLO not just HELLO; (3) you saved as hello.lsp not hello.lsp.txt — show file extensions in Explorer to confirm.
What does ( / ) mean?
Everything before / is positional arguments; everything after is local variables. ( / x y ) declares no arguments and two locals x and y. Locals shadow globals while the function runs and are released after.
Why two (princ)?
The first is your message. The second, with no arguments, returns nothing visibly — without it AutoLISP would echo the return value of the last expression to the command line, which looks ugly.
How do I read user input?
(getstring "Enter your name: ") or (getreal "Enter a number: ") or (getpoint "Pick a point: "). The result is stored in a variable: (setq name (getstring "Name: ")).
Where can I go next?
Read the AutoLISP Reference (F1 → AutoLISP), Lee Mac's tutorials, and AfraLISP's introductory pages. Pick up George Omura's book if you want a structured path.
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.
AutoLISP explained from scratch — what it is, why it's still relevant 40 years later, and when to choose it over .NET.
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Related terms
Autodesk's dialect of LISP, built into AutoCAD since 1986, used to write custom commands and automate drawings.
A self-contained AutoLISP program that adds a command or behaviour to AutoCAD — usually one .lsp/.fas file.
The AutoCAD command that opens a dialog for loading .lsp, .fas, .vlx, .arx, or .dll files into the current session.