On-device generation in Chrome

The public web editor can turn a short description into a new diagram using Chrome’s built-in model, Gemini Nano, through the Prompt API. The model runs on your device: no account, no server, and nothing you type leaves your machine.

The model never writes BPMN XML. It writes BPMN Kit’s line-based process text, which parseProcessText repairs and the editor draws while the text streams in.

What it does

While the Prompt API is an origin trial, the feature is opt-in: open the editor at /editor?ai=on-device. Without that parameter the editor does not load it.

A Generate button and a Generate dock tab appear in the editor. Where the browser has no on-device model, neither appears and nothing is logged.
Type a description (up to 2,000 characters) and press Generate. A new tab opens, named from the # Process name line, and its diagram grows as lines arrive. Your open diagrams are never changed.
When the run ends, the panel lists the parser’s problems and fixes. The tab holds a valid, laid-out diagram.
Stop aborts the run and keeps what was drawn. Switching to another tab during a run also stops it, so no frame lands in the wrong diagram.

Limits: English only, and generate only. There is no editing of an existing diagram and no chat.

Requirements

Desktop Chrome: Windows 10/11, macOS 13+, Linux, or a ChromeOS Chromebook Plus.
More than 4 GB of VRAM, 16 GB of RAM and at least 22 GB of free disk space.
A one-time model download, which needs an unmetered network.
Web pages need the Prompt API origin trial (Chrome 148). Extensions and local flags do not.

Enable it locally

Open chrome://flags and set Prompt API for Gemini Nano (#prompt-api-for-gemini-nano) to Enabled.
Restart Chrome.
Optional: open chrome://on-device-internals to check whether the model is available on this device.
Open the editor at /editor?ai=on-device.

The first Generate downloads the model once; the panel shows the progress. If Chrome cannot prepare the model (for example, no disk space), the panel says why.

Messages

Case	Message
Description too long	”Description too long for the on-device model — shorten it.” Nothing is sent.
Model could not be prepared	”Chrome couldn’t prepare the on-device model: reason”
Context overflow mid-run	”The diagram outgrew the model’s context — try a smaller process.” The partial tab is kept.
Stream error	”Generation failed: reason”. The partial tab is kept.
Prose instead of a diagram	”The model didn’t return a diagram — try rephrasing.” No tab opens.

Embed it

import { createAiLocalPlugin } from "@bpmnkit/plugins/ai-local";

const aiLocal = createAiLocalPlugin({
  // First streamed frame: open a new tab.
  openDiagram: (xml, name) => {
    generatedTabId = openTab({ type: "bpmn", xml, name });
  },
  // Later frames and the final result: redraw that tab. Guard on the active
  // tab so a frame never lands in a diagram the user switched to.
  updateDiagram: (defs) => {
    if (getActiveTabId() !== generatedTabId) return;
    editor.loadDefinitions(defs);
    hud.hideOnboarding(); // loadDefinitions does not lift the onboarding overlay
  },
  container: dock.generatePane, // optional; defaults to document.body
  onOpen: () => dock.switchTab("generate"), // optional; runs when the button is clicked
});

// `ready` is true when the model is available or can be downloaded.
if (await aiLocal.ready) {
  dock.setGenerateTabVisible(true);
}

// The button stays hidden until `ready` resolves true; the HUD places it.
const hud = initEditorHud(editor, { generateButton: aiLocal.button });

// Call stop() when the user switches tabs mid-run.
aiLocal.stop();

ready resolves true for the available, downloadable and downloading states, and false otherwise. To serve the feature on your own site, register the origin for the Prompt API origin trial and add the token in an origin-trial meta tag.

In Drop

Add ?ai=on-device to Drop’s page (/drop?ai=on-device) and “Describe a process” drafts on the device: no access code, no challenge, no request to Drop’s server. The follow-up steps that call the server stay off in this mode: the check for missing elements, connector configuration, drafting from an image and change requests. Share still works. Where the model isn’t available, the page says so and keeps using Drop’s server as usual.

Manual test checklist

Generate three different descriptions; each opens a new tab with a valid diagram.
Press Stop mid-run; the partial diagram stays and the status reads “Stopped”.
Switch tabs mid-run; the run stops and no frame lands in the other tab.
Close the generated tab mid-run; nothing breaks.
Paste a 2,000-character description; it is accepted or gives the “too long” message.