How do AI shopping agents check out?
An AI agent checks out in one of two ways. It either talks to the store through a machine-readable protocol like UCP or ACP and gets a checkout link or session, or it drives a web browser like a person, adding to cart and filling forms. Payment usually still needs the buyer's approval. ARC measures both routes.
Two routes: protocol lane and browser lane
The protocol lane is an HTTP check. ARC asks the store's catalog tool for a product, then asks for a checkout link. The browser lane is five ARC browser shoppers that try to add that product to the cart. Both stop before payment. The method is written up in How ARC tests. Method, as published on /blog/how-arc-tests and /methodology. Label: Measured (method).
Step by step: find, cart, checkout, pay
Find the product. Put it in a cart, which on a web page can mean choosing a size or colour first. Reach a checkout link or a checkout page. Payment is a separate step. In the checkout WebMCP tools ARC detects, completion asks for the buyer's approval.
Where the buyer approves
ARC's checkout WebMCP note is HTML detection only: the page declares get, update and complete tools, and completion requires buyer approval. That is not a live agent session and not a purchase. WebMCP transacts on the Protocol Matrix is Inferred, because it links two observations. It does not prove the tool was used.
ARC saved checks, accessed 2026-10-13
Declared: 1,680 of 4,307 (39%)MeasuredWebMCP adapter found in server HTML
Valid: Not measuredNot measuredNot checked (no live browser session)
Usable: Not measuredNot measuredNot checked (no live browser session)
Transacts: 39 of 51 (76.5%)InferredIndex stores with WebMCP where at least one browser shopper reached the cart
Where it breaks
ARC open dataset snapshot 2026-10-12. Index browser tests stop at add-to-cart. Nothing is bought.
Measured scored stores: 77MeasuredA published score whose dataset row is evidence=measured. Rates below use only these stores.
Inferred scores: 6InferredKept out of the rates. An inferred score is not treated as a failure or a success.
No published score: 6Not measuredRetest pending or not finished. A missing score is not a zero, and it is not a mark against the store.
5 of 5 shoppers added to cart: 32 of 77Measured
0 of 5 shoppers added to cart: 18 of 77Measured
0 of 5, but a checkout link still came back: 13 of 18MeasuredMeasured scores only, snapshot 2026-10-12. Inferred scores and stores with no published score are outside this count. The protocol check said yes. The browser test did not get the product into the cart.
Median score: 83Measured
Highest score in this snapshot: 86 of 100MeasuredIndex tests stop at add-to-cart, so a clean cart pass does not score 100. The formula is on the methodology page.
Published stop reason where at least one shopper missed add-to-cart (45 of 77 Measured stores):
| Stop reason | Stores |
|---|---|
| Couldn't add it to the cart | 32 |
| Blocked at the size picker | 8 |
| Stopped by a human-check | 3 |
| Store blocks automated agents at the door | 2 |
| Shoppers that added to cart | Measured stores |
|---|---|
| 0 of 5 | 18 |
| 1 of 5 | 6 |
| 2 of 5 | 1 |
| 3 of 5 | 2 |
| 4 of 5 | 18 |
| 5 of 5 | 32 |
What this means for stores
A checkout link and a working add-to-cart button are different. Fix the stop the browser test recorded, and keep the catalog check. Then retest.
Frequently asked questions
- How do AI shopping agents check out?
- An AI agent checks out in one of two ways. It either talks to the store through a machine-readable protocol like UCP or ACP and gets a checkout link or session, or it drives a web browser like a person, adding to cart and filling forms. Payment usually still needs the buyer's approval. ARC measures both routes.
- Does the AI pay without asking me?
- In the flows ARC sees, checkout tools require the buyer's approval before completing.
- Do agents use the same checkout as people?
- Sometimes. Browser agents use the normal site; protocol agents use a checkout link or session the store returns.
- Where do agents fail most?
- In ARC's Index, most stops happened at the add-to-cart step. The current counts are on this page.
- Does ARC complete purchases?
- No. ARC stops before payment and never places orders.
On ARC
Cite this: ARC, arcreport.ai, accessed 2026-10-13, CC-BY-4.0. Protocol figures: ARC saved checks, accessed 2026-10-13 (13 October 2026). Index browser figures: ARC open dataset snapshot 2026-10-12. Platform figures: ARC saved checks, accessed 2026-10-13.
Every figure is labelled Measured, Inferred or Not measured. Not measured is not zero. A missing result is not a mark against a store. ARC stops before payment.