Browser Extension
A Chrome side panel that runs an agent session on the tab you are already looking at. The storefront stays on the left; every tool call, argument, response and timing the agent actually received renders on the right.
The extension drives the same orchestrator as the Agent page, through the Headless API — so a session started beside a product page behaves exactly like one started in the Playground, and any improvement to agent behavior lands in both for free. When the tab's domain publishes a UCP manifest, the panel connects automatically; when it doesn't, it tells you that too.
Add it to Chrome ↗ — it's free, and works with your existing Playground account.
Set up in four steps
- Install the extension — from the Chrome Web Store ↗. It opens as a side panel pinned to the right of the browser.
- Sign in to the Playground — the extension authenticates against your own account, so sessions it runs show up in your session history like any other.
- Create a personal access token — under Settings → API tokens. This is the only credential the extension needs.
- Paste it into the extension's options — click the extension icon → options, paste the token, and pick a default model. The token is stored in your browser's extension storage and sent only to the Playground API.
Debug your own store against the human version
The two-pane layout is the point. When your product page says one thing and get_product_details says another, the disagreement is on screen — the human version of your store beside the machine version, with nothing summarized away. Stale prices, missing variants, a cart that ignores line_items: these are exactly the bugs that hide when you only ever look at one side.
Because the panel rides along as you browse, you can navigate to the page a customer would actually be on, ask the agent for the same product, and compare what each of you was told.
Watch other stores in real time
It works on any target, not just yours. Open any store that publishes a /.well-known/ucp manifest and the panel detects it, connects, and lets you read its payloads live while you browse — a fast way to see how other merchants shape their catalogs, carts and checkout handoffs before you shape your own.
What the extension can and can't see. It never reads page content. Its host permissions cover exactly three things: probing /.well-known/ucp to detect manifests, talking to the Playground API, and localhost for development. Your token stays in the browser's extension storage, and chat traffic goes only to the Playground — the merchant is reached through the same server-side transports as every other session.
The extension talks to the store's UCP endpoint only. It doesn't use the tools a store page registers through WebMCP; to run an agent through those, use the Agent page's Connection picker (see WebMCP: the store page).
Which surface, when
The extension is the third way to drive the harness, not a replacement for the first two:
| Surface | Best for |
|---|---|
| Inspector | Calling individual tools by hand and debugging raw request/response shapes — no model in the loop. Its WebMCP view lists the store page's own tools beside the UCP ones. |
| Agent | Full autonomous sessions with the live funnel, info rail, debug console and multi-model comparison, over UCP or through the store page's WebMCP tools. |
| Extension | Sessions beside the real storefront in your own browser — your store during development, or any UCP store while you browse it. |
Checkout hands off to the merchant's own continue_url in a new tab, so payment always happens on the store's turf — the extension never touches payment details.