Guide · Grasshopper

Grasshopper, in 10 minutes.

The mental model that makes everything click. Read this before Session 2 and you'll walk in already understanding what you're looking at.

The big idea: build the rule, not the thing

In normal modeling you draw a building. In Grasshopper you draw the rule that draws the building. Change the rule, and everything updates — instantly. Want the façade panels bigger? Move one slider. Want ten variations? You already have them.

Reframe: Grasshopper is not coding. It's a diagram of rules — the same way architects already think. "If the site slopes, step the floors" is a parametric rule. You'll just be drawing those rules instead of describing them.

The three parts you'll see

Every Grasshopper definition is made of three kinds of things:

  • Components — the boxes. Each one does something: make a point, draw a circle, move geometry. Think of them as verbs.
  • Parameters — values you set, like a Number Slider. These are the dials you turn.
  • Wires — the lines connecting boxes. They carry data from one component's output to the next one's input.

Data flows left to right

Read a Grasshopper definition like a sentence: inputs on the left, outputs on the right, data flowing rightward along the wires. A slider feeds a number into a circle's radius; the circle feeds its shape into an extrude; the extrude feeds a solid into the output. One direction, one flow.

The one habit: always look at your data

Beginners get lost because they can't see what's flowing through the wires. The fix is one component:

  • Drop a Panel onto any output to read the actual numbers or text.
  • Drop a Param Viewer to see the structure of the data.

Keep a Panel on screen at all times when you're learning. If something looks wrong, look at the data before you touch anything else.

A word on data trees (don't panic)

Grasshopper organizes data in lists (a row of values) and trees (branches of lists — what you get from a grid). Trees are the one thing that trips everyone up, which is exactly why we give them a full session (Session 3). For now, just know the three magic words you'll hear:

  • Flatten — squash everything into one list.
  • Graft — put each item in its own branch.
  • Simplify — clean up messy nesting.

That's all you need before class. We'll make them second nature together.

Before Session 2

  1. Make sure Rhino + Grasshopper are installed — see the Installation Guide.
  2. Open Grasshopper once and drag a few components around so the canvas isn't unfamiliar.
  3. Optional: grab the free attractor mini-lesson to see a real definition in action.
Come to Session 2 with this mental model — components, wires, data left-to-right, always look at your data — and the "it's alive" moment will land instantly.