First Layout

This guide picks up right after Installation. You already have a project created with rosette init. Now you will write your first design script, build a GDS file, and view it in the browser.

If any of the concepts below feel new, skim the Core Concepts page first. Everything on this page is explained there in more depth.

Create a design file

After rosette init your project has an empty designs/ directory. Create a new Python file there:

touch designs/hello.py

Open designs/hello.py in your editor and add the following:

# designs/hello.py
from rosette import Cell, Layer, Point, Polygon, Port, Vector2
from rosette.io import write_gds

# 1. Create a top-level cell.
top = Cell("hello")

# 2. Add a waveguide: a 50 x 0.5 um rectangle on layer 1/0.
wg = Polygon.rect(Point(0, -0.25), 50, 0.5)
top.add_polygon(wg, Layer(1, 0))

# 3. Add a label on layer 10/0.
top.add_text("hello", Point(0, 2), Layer(10, 0), height=1.0)

# 4. Mark the waveguide endpoints as ports.
top.add_port(Port("in",  Point(0,  0), Vector2(-1, 0), width=0.5))
top.add_port(Port("out", Point(50, 0), Vector2( 1, 0), width=0.5))

# 5. Write it to GDS.
write_gds("output/hello.gds", top)

That is everything, five short steps. Let's break down what each line does before we run it.

What's going on

• Cell("hello") creates an empty Cell named hello. This is your top-level design.
• Polygon.rect(origin, width, height) builds a rectangle whose lower-left corner sits at origin. Centering it on y = 0 makes the waveguide symmetric about the X axis.
• Layer(1, 0) is GDS layer 1/0. The CLI's default config treats layer 1/0 as the silicon waveguide layer and layer 10/0 as text.
• add_text writes a label on the text layer. Labels are useful for debugging and are typically not fabricated.
• Port(name, position, direction, width) marks a connection point. direction is a unit vector pointing outward from the component. The input faces -X, the output faces +X. Width matches the waveguide.
• write_gds serializes the cell to a GDS file.

Build and view

You have two ways to see the result: build a GDS file and open it in the viewer, or run the dev server for live reload while you edit.

Live preview (recommended)

uv run rosette serve designs/hello.py

The dev server opens http://localhost:5173/preview in your browser with an interactive WebGPU viewer. Every time you save designs/hello.py the viewer reloads automatically, so you can tweak the script and see the result immediately. The Python file remains the source of truth, so the live viewer is read-only. Use Edit a copy when you intentionally want to detach the rendered layout into an editable app document. See Editing and Persistence for the full save and export contract.

One-shot build

If you just want the GDS file:

uv run rosette build designs/hello.py

The output is written to output/hello.gds. Open it later with uv run rosette run output/hello.gds.

What you should see

A 50 um long, 0.5 um wide pink rectangle centered on the X axis, with the word hello rendered just above it on a different layer. Two port markers sit at the ends of the waveguide, pointing outward.

Extend it

Now that you have a working build, try a few small edits and watch them update live:

• Change the rectangle's width to 100 to make a longer waveguide.
• Add a second Cell and reference it from top with top.add_ref(child.at(x, y)). See the Cells & Hierarchy guide.
• Replace the hand-built rectangle with a connected Route between two ports. See the Routing guide.
• Define named layers in rosette.toml and load them with load_layer_map() so you can write layers.silicon.layer instead of Layer(1, 0).

Where to next