ARC · METHODOLOGY

Metrics glossary

How to cite ARC headline figures: what each count measures, the number, what it is out of, the date, and what it does not show.

Cite a figure with its number, what it is out of, and its date or snapshot. A percentage without those three is not a citation.

Unpublished drafts are not cited. Use the live adoption feed or a dated snapshot.

Checkout link (live)

Checkout link (live): 7,297 of 11,410 stores checked (64.0%), as of 17 Oct 2026, 02:13 UTC. Counts stores where the latest check got a checkout link with an item in the cart. Doesn't show that checkout loaded, payment works or an order can be placed.

What it counts
Counts stores where the latest check got a checkout link with an item in the cart.
Number
7,297 (64.0%)
Out of
11,410 stores checked
As of
17 Oct 2026, 02:13 UTC
What it doesn't show
Doesn't show that checkout loaded, payment works or an order can be placed.

Valid UCP profile (live)

Valid UCP profile (live): 8,319 of 11,410 stores checked (72.9%), as of 17 Oct 2026, 02:13 UTC. Counts stores where the latest check found a valid UCP profile. Doesn't show that a checkout link came back, that checkout loaded, or that an order can be placed.

What it counts
Counts stores where the latest check found a valid UCP profile.
Number
8,319 (72.9%)
Out of
11,410 stores checked
As of
17 Oct 2026, 02:13 UTC
What it doesn't show
Doesn't show that a checkout link came back, that checkout loaded, or that an order can be placed.

Shopify stores (live)

Shopify stores (live): 8,199 of 11,410 stores checked (71.9%), as of 17 Oct 2026, 02:13 UTC. Counts stores checked whose platform was measured as Shopify. Doesn't show how stores on other platforms behave. Checkout link and valid profile rates for these Shopify stores are separate cards.

What it counts
Counts stores checked whose platform was measured as Shopify.
Number
8,199 (71.9%)
Out of
11,410 stores checked
As of
17 Oct 2026, 02:13 UTC
What it doesn't show
Doesn't show how stores on other platforms behave. Checkout link and valid profile rates for these Shopify stores are separate cards.

Checkout link, Shopify stores (live)

Checkout link, Shopify stores (live): 7,242 of 8,199 Shopify stores checked (88.3%), as of 17 Oct 2026, 02:13 UTC. Counts Shopify stores where the latest check got a checkout link with an item in the cart. Doesn't show that checkout loaded, payment works or an order can be placed.

What it counts
Counts Shopify stores where the latest check got a checkout link with an item in the cart.
Number
7,242 (88.3%)
Out of
8,199 Shopify stores checked
As of
17 Oct 2026, 02:13 UTC
What it doesn't show
Doesn't show that checkout loaded, payment works or an order can be placed.

Valid UCP profile, Shopify stores (live)

Valid UCP profile, Shopify stores (live): 8,098 of 8,199 Shopify stores checked (98.8%), as of 17 Oct 2026, 02:13 UTC. Counts Shopify stores where the latest check found a valid UCP profile. Doesn't show that a checkout link came back, that checkout loaded, or that an order can be placed.

What it counts
Counts Shopify stores where the latest check found a valid UCP profile.
Number
8,098 (98.8%)
Out of
8,199 Shopify stores checked
As of
17 Oct 2026, 02:13 UTC
What it doesn't show
Doesn't show that a checkout link came back, that checkout loaded, or that an order can be placed.

Checkout link (snapshot 2026-10-12.r3)

Checkout link (snapshot 2026-10-12.r3): 1,311 of 3,318 completed checks (39.5%), as of snapshot 2026-10-12.r3, generated 13 Oct 2026, 19:30 UTC. Counts completed checks in this snapshot where the check got a checkout link with an item in the cart. Doesn't show that checkout loaded, payment works or an order can be placed.

What it counts
Counts completed checks in this snapshot where the check got a checkout link with an item in the cart.
Number
1,311 (39.5%)
Out of
3,318 completed checks
As of
snapshot 2026-10-12.r3, generated 13 Oct 2026, 19:30 UTC
What it doesn't show
Doesn't show that checkout loaded, payment works or an order can be placed.

Valid UCP profile (snapshot 2026-10-12.r3)

Valid UCP profile (snapshot 2026-10-12.r3): 1,601 of 3,318 completed checks (48.3%), as of snapshot 2026-10-12.r3, generated 13 Oct 2026, 19:30 UTC. Counts completed checks in this snapshot where the UCP profile passed validation. Doesn't show that a checkout link came back, that checkout loaded, or that an order can be placed.

What it counts
Counts completed checks in this snapshot where the UCP profile passed validation.
Number
1,601 (48.3%)
Out of
3,318 completed checks
As of
snapshot 2026-10-12.r3, generated 13 Oct 2026, 19:30 UTC
What it doesn't show
Doesn't show that a checkout link came back, that checkout loaded, or that an order can be placed.

Checkout link, Shopify stores (snapshot 2026-10-12.r3)

Checkout link, Shopify stores (snapshot 2026-10-12.r3): 1,266 of 1,561 completed Shopify stores (81.1%), as of snapshot 2026-10-12.r3, generated 13 Oct 2026, 19:30 UTC. Counts completed Shopify stores in this snapshot where the check got a checkout link with an item in the cart. Doesn't show that checkout loaded, payment works or an order can be placed.

What it counts
Counts completed Shopify stores in this snapshot where the check got a checkout link with an item in the cart.
Number
1,266 (81.1%)
Out of
1,561 completed Shopify stores
As of
snapshot 2026-10-12.r3, generated 13 Oct 2026, 19:30 UTC
What it doesn't show
Doesn't show that checkout loaded, payment works or an order can be placed.

Checkout link, stores not detected as Shopify (snapshot 2026-10-12.r3)

Checkout link, stores not detected as Shopify (snapshot 2026-10-12.r3): 45 of 1,757 completed stores not detected as Shopify (2.6%), as of snapshot 2026-10-12.r3, generated 13 Oct 2026, 19:30 UTC. Counts completed stores in this snapshot not detected as Shopify where the check got a checkout link with an item in the cart. Doesn't show that checkout loaded, payment works or an order can be placed.

What it counts
Counts completed stores in this snapshot not detected as Shopify where the check got a checkout link with an item in the cart.
Number
45 (2.6%)
Out of
1,757 completed stores not detected as Shopify
As of
snapshot 2026-10-12.r3, generated 13 Oct 2026, 19:30 UTC
What it doesn't show
Doesn't show that checkout loaded, payment works or an order can be placed.

What 'reaches checkout' means on ARC: a saved check got a checkout link back from the store's agent connection. ARC does not open that checkout page, pay or place an order.

  • The note stored with a check says the checkout page was not opened, including when a checkout link came back. Older notes are published with the current sentence.
  • Index scans stop once the item is in the cart. The score formula has a further step for a checkout page. Index scans do not record that step.
  • A checkout link is recorded as returned. The check does not open that link.
  • A separate Shopify check reads the checkout page for declared tool names. It does not call those tools and does not send shopper data. It is not part of the checkout-link count.
  • Some other runs can open the checkout page and stop before payment. Those runs are not Index scans, and they are not a count on this page.
For developers: where this is computed

A checkout link is computed in src/lib/rails/check.ts. checkStoreRails calls the cart tool, then sets cartOutcome to link only when the tool payload is not an error, cartContinueUrl finds an https continue_url or continueUrl, and cartHasLineItem finds at least one line. facts.cartLink is that same result. The cart tool is create_cart on the UCP endpoint when that tool is listed. Otherwise it is legacy storefront update_cart. UCP update_cart is not called. When the payload includes a cart id and cancel_cart is listed, the check calls cancel_cart afterwards. The stored flag stays link either way. The URL is redacted and is not written to the database. agent_rails.cart_status stores the word link.

The live cards read GET /api/agent-checkout/adoption, the same feed as /agent-checkout/adoption and the agent_commerce_adoption tool. loadAdoption in src/lib/rails/adoption-load.ts keeps listed hosts only, the same set as the directory and the Protocol Matrix. summarize in src/lib/rails/adoption.ts sets checkoutLink when cartStatus is the string link, and validUcpProfile when ucpProfile is valid, on the latest completed row per host. hostsChecked is that completed set. A failed latest attempt is not the denominator. An earlier completed row stays in use after a later failure. The percentage is Math.round(count / hostsChecked × 1000) / 10. asOf is the newest checkedAt among those completed rows. The route revalidates hourly, so a later read can move. Platform cards use byPlatform for the measured Shopify pool. That pool's checkoutLink and validUcpProfile rates use the Shopify host count as their out-of number, not every store checked.

The snapshot cards use the same files as /data. loadDataPageCounts in src/lib/dataset/data-page.ts reads public/data/latest/store_answers.csv and checks it against summary.json and manifest.json. Cite the version folder, not only latest/. Checkout link yes is can_agents_get_checkout_link = yes, manifest headline.checkout and headline.checkoutPct, out of headline.tested. Valid UCP profile yes is ucp_profile_valid = yes, headline.ucp and headline.ucpPct. Shopify checkout is headline.shopifyCheckout of headline.shopify. Stores not detected as Shopify are headline.otherCheckout of headline.otherPlatforms. generated_at on the manifest is the snapshot's as-of time.

A valid profile is parseUcpProfile in src/lib/rails/parse.ts returning valid. The /.well-known/ucp body parses as JSON, ucp.version is a YYYY-MM-DD string, and ucp.services has an entry with a transport, an endpoint, or a version string. An HTML page or a block is not valid. invalid, absent, blocked, and error are not in the numerator. On the snapshot, storeAnswerStats in src/lib/dataset/answers.ts counts ucp_profile_valid yes among completed rows.

Saved proves sentences for a reachable check end with REACHABLE_CHECKOUT_CLAUSE in src/lib/precheck/reachable-proves.ts (ARC did not reach checkout in this check). That clause means this check did not open the checkout page. It is still appended when a checkout link was returned. Rows that stored an older ending are published with the current sentence.

The Index scan plan is depth cart in src/lib/index/refresh.ts. That plan stops once the item is confirmed in the cart. The score formula has a depth named reached checkout. Index scans do not produce that depth. checkoutLink does not fetch the continue URL.

Checkout WebMCP is a separate read of Shopify checkout HTML. It looks for declared tool names get_checkout, update_checkout, and complete_checkout. It does not call those tools and does not send shopper data. It is not included in the checkout-link count. A browser plan depth named checkout exists for other runs and stops before payment. It is not the Index scan, and it is not a numerator on this page.

Unpublished worker drafts are written up in docs/metrics-unpublished-drafts.md in the repository. This page does not cite them.

Cite: ARC method arc-method-2026.10, arcreport.ai/methodology/metrics. CC-BY-4.0. Citation file: CITATION.cff. Method changes: changelog. Dataset: /data. Live feed: adoption.