diff --git a/Cargo.lock b/Cargo.lock
index 68886af..6c19a55 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2744,6 +2744,7 @@ version = "0.1.0"
 dependencies = [
  "eframe",
  "petri",
+ "rand",
 ]
 
 [[package]]
diff --git a/uscope/Cargo.toml b/uscope/Cargo.toml
index df2f989..c5f5ad4 100644
--- a/uscope/Cargo.toml
+++ b/uscope/Cargo.toml
@@ -8,3 +8,4 @@ edition = "2021"
 [dependencies]
 petri = { path = "../petri" }
 eframe = "0.27.2"
+rand = "0.8.5"
diff --git a/uscope/src/main.rs b/uscope/src/main.rs
index 7c26fb9..a71cb9d 100644
--- a/uscope/src/main.rs
+++ b/uscope/src/main.rs
@@ -1,8 +1,10 @@
 use eframe::{
 	egui::{CentralPanel, Color32, Painter, Pos2, Rect, Sense, SidePanel, Slider, Ui, Vec2},
+	epaint::Hsva,
 	NativeOptions,
 };
 use petri::{Cell, Chunk, Dish, Rule, RulePattern, CHUNK_SIZE};
+use rand::prelude::*;
 
 fn main() {
 	eframe::run_native(
@@ -53,12 +55,20 @@ impl eframe::App for UScope {
 			ui.heading("Cells");
 			for (i, cell) in self.celltypes.iter_mut().enumerate() {
 				ui.horizontal(|ui| {
-					ui.set_width(100.);
+					ui.set_width(120.);
 					ui.radio_value(&mut self.brush.0, i as u16, "");
 					ui.text_edit_singleline(&mut cell.name);
 					ui.color_edit_button_srgba(&mut cell.color);
 				});
 			}
+			if ui.button("add cell").clicked() {
+				let h = random::<f32>();
+				let s = random::<f32>() * 0.5 + 0.5;
+				let v = random::<f32>() * 0.5 + 0.5;
+				let color = Hsva::new(h, s, v, 1.).into();
+				let name = format!("cell #{}", self.celltypes.len());
+				self.celltypes.push(CellData { name, color })
+			}
 			ui.heading("Rules");
 			for rule in &mut self.dish.rules {
 				rule_editor(ui, rule, &self.celltypes);