Your first commands

The turtle starts in the centre, facing up. Type into the command prompt and press Enter. Distances are screen units; turns are in degrees.

REPEAT 4 [FD 100 RT 90]

To write a longer program, use the editor and select Run program (Ctrl+Enter). Each full run starts with a fresh turtle and variables. Prompt commands keep the current drawing and routines. Pause freezes execution; Resume continues it. Stop or Esc ends the running program.

Teach the turtle a new word

TO SQUARE :SIDE
  REPEAT 4 [FD :SIDE RT 90]
END

SQUARE 120
SQUARE 60

TO … END defines a routine. :SIDE is its input. Commands can be upper or lower case. A semicolon begins a comment that lasts to the end of the line.

A desk-side command card

`FD 100 / BK 100`	Forward / back
`RT 90 / LT 90`	Right / left
`PU / PD`	Pen up / down
`CS / CLEAN / HOME`	Clear and home / clear only / move home
`HT / ST`	Hide / show turtle
`SETXY 50 -80`	Move to X, Y; draws if pen is down
`SETH 90`	Face east; 0 is up
`SETPC 6`	Cyan pen; colour names also work: `SETPC "red`
`SETPENSIZE 3`	Pen width
`SETBG "black`	Background colour
`REPEAT 10 [FD 20 RT 36]`	A counted loop; `REPCOUNT` is the iteration number
`FOREVER [FD 1 RT 1 WAIT 1]`	Loop until Stop; `DOFOREVER` is an alias
`MAKE "SIZE 100`	Store a value; read it with `:SIZE`
`IF :SIZE < 5 [STOP]`	Conditional; STOP returns from the current routine
`IFELSE :X > 0 [RT 90] [LT 90]`	Choose between two blocks
`PRINT [Hello again]`	Write to the text output
`SHOW POS`	Show the turtle's position as a list
`WAIT 60`	Wait one second (60 ticks)
`WRAP / WINDOW / FENCE`	Wrap at edges / draw offscreen / stop at edges

Variables, lists and arithmetic

MAKE "N 6
PRINT :N * 7
MAKE "POINT [10 20 30]
PRINT ITEM 2 :POINT

TO DOUBLE :N
  OUTPUT :N * 2
END
PRINT DOUBLE 21

Use (LOCAL "A "B) for variables local to a routine, or LOCALMAKE "A 10. Lists use square brackets. FIRST, LAST, BUTFIRST, COUNT, LIST, SENTENCE and ITEM work with words or lists as appropriate. ITEM counts from 1. Expressions support +, −, *, /, comparisons, RANDOM, SQRT, SIN and COS. Trigonometry uses degrees. Use parentheses to make grouping clear.

How the spinning cube works

The first example is an actual Logo program. SPINCUBE defines eight 3D vertices and twelve edges. EDGE lifts the pen, projects one endpoint, then draws to the other. PROJECT rotates each point using SIN and COS, and divides by depth to make distant points appear smaller. Only ordinary 2D turtle commands draw the result.

The outer FOREVER redraws the cube, while REPEAT 12 draws its edges. WAIT 2 presents each completed frame. Change MAKE "A :A + 2 to + 4 for faster rotation, or use WAIT 4 for slower playback. Change SETPENCOLOR "cyan to "yellow. Stop, edit, then Run.

Keep what you make

The editor is saved automatically on this device when browser storage is available. Save .logo creates a portable text file of the editor; Open .logo loads one. Routines typed only at the prompt live in the current session, so put anything you want to save in the editor. Save image exports the drawing as PNG. Keep offline downloads the complete app as a single HTML file. Double-click that file in Edge or Chrome; it needs no installation or internet connection.

A familiar flavour of Logo

This is a modern browser Logo, inspired by the BBC computer room. It is not an exact Acornsoft emulator. It uses Joshua Bell's jslogo interpreter, a broad subset of UCBLogo, with the BBC colour order: 0 black, 1 red, 2 green, 3 yellow, 4 blue, 5 magenta, 6 cyan, 7 white. DRAW resets the screen and turtle. Classic movement, loops, routines, lists and recursion are supported; BBC sound, hardware and disk commands are not emulated.

Interpreter and turtle engine © Joshua Bell and contributors, Apache License 2.0. Original interpreter · Full language reference. The offline file includes the licence and modification notes.

What shall we make today?