diff --git a/docs/12-design-journey.md b/docs/12-design-journey.md
index 749df8b..679eda1 100644
--- a/docs/12-design-journey.md
+++ b/docs/12-design-journey.md
@@ -32,6 +32,11 @@ for. Starting from a picture gives an anchor before building anything.
 > - [`prototype/src/sim.ts`](https://git.produktor.io/eSlider/swarm-house/src/branch/main/prototype/src/sim.ts#L219-L287) — the tick: links form and break by range, pose broadcasts and bulk sync accumulate bytes
 > - [`prototype/src/sim.ts`](https://git.produktor.io/eSlider/swarm-house/src/branch/main/prototype/src/sim.ts#L57-L63) — the pose-frame size and rate that drive the volume estimate
 
+The picture is running, not just described: the visual prototype is live at
+[swarm.produktor.io](https://swarm.produktor.io/) (same access as this
+repository). It draws units patrolling, links forming and breaking by range, and
+a running estimate of how much data crosses the air.
+
 ## 3. Naming the limits
 
 Before any code, the limits had to be named. Maximum distance between units in