L-system Generator

A Lindenmayer system (L-system) is a string-rewriting grammar: you start with an "axiom" string, and repeatedly replace every character that has a matching rule, all at once, for a number of iterations. The resulting string is then drawn as turtle graphics to produce a fractal shape.

F and G move the turtle forward one step and draw a line; f moves forward without drawing. + turns left and - turns right, both by the configured angle. [ pushes the current position and heading onto a stack (for branching), and ] pops it back off. Any other letter (commonly X or Y) has no direct drawing effect — it exists purely so rewrite rules can shape the expansion, as in the classic fractal-plant example.

Many L-system rules grow exponentially (e.g. F=FF roughly doubles the string every iteration), so without a cap a high iteration count could generate a string with millions of characters and hang the browser. The expansion is also hard-capped at 300,000 characters and drawing at 50,000 line segments — if either limit is hit you'll see a truncation warning instead of a frozen tab.

Yes — edit the Axiom, Rules, Iterations, Angle, and Step length fields directly. Rules are one per line in A=AB or A->AB form (the left side must be a single character); any character without a matching rule passes through unchanged during expansion.

Yes. Click Share to copy a URL that encodes the current axiom, rules, iterations, angle, and step length, so anyone who opens the link sees the same fractal.