ACK-Pay (Agent Commerce Kit) vs Universal Commerce Protocol (UCP)

ACK-Pay (Agent Commerce Kit) 38

Graded as a protocol on reference implementations (30), public servers or processors (25), spec stability (25) and test vectors (20). One reference SDK in TypeScript at 0.11.0, with a payments demo and example issuer and verifier services in the repository (15). No public Payment Service or Receipt Service was found. The docs use example.com hosts and the demo settles on Base Sepolia, Solana devnet or a simulated Stripe payment (0). The versioning page names 2025-05-04 as the current stable protocol version and says the date changes only on incompatible changes, but the specification is prose documentation without normative language and the SDK is below 1.0 (15). No test vectors are published, and the specification still names 2025-05-04 as the current version on 4 November. The ack-pay package has seven unit test files, and the Check workflow passed on the last five pushes to main on the page read on 9 October, not re-read on 4 November; the workflow still runs build, lint and the vitest suites on every push and pull request (8). 15 + 0 + 15 + 8 = 38.

Universal Commerce Protocol (UCP) 79

Protocol reading, split as reference implementations 30, live deployments 25, spec stability 25 and test vectors 20. Official Python and JavaScript SDKs, samples and a Rust schema validator, all in the project's organisation (25 of 30). Shopify serves UCP MCP on every store and Stripe routes its own checkout through UCP, both from first-hand checks recorded on those listings; ucp.dev lists about 50 endorsers, which are claims (20 of 25). Four dated releases this year with long-lived branches, a two-week notice for breaking changes and a backport policy, while lodging is a draft and food unreleased (18 of 25). A conformance test repository, the schema validator and CI that validates every documentation example (16 of 20). 25 + 20 + 18 + 16 = 79.

ACK-Pay (Agent Commerce Kit) 47

A paid call takes a 402, a call to a Payment Service, a receipt and a retry, which is one party more than a direct 402 scheme. A receipt can be reused until it expires (15). A request can carry several payment options, there are server-initiated and client-initiated sequences and an optional serviceCallback, and no session or metering scheme is defined (12). No protocol error codes. The SDK throws two named error classes and the operations page asks implementers to write their own error taxonomy (5). The request id is there to stop replay and verifiers are told to reject reused receipts, with no idempotency key (8). One SDK, in TypeScript (7). 15 + 12 + 5 + 8 + 7 = 47.

Universal Commerce Protocol (UCP) 82

Protocol reading. Capability negotiation means an agent sees only what both sides support, though the schemas are large (18 of 25). Catalogue search pages with a cursor and has_next_page (15 of 20). An error model with codes and continue_url to hand a buyer to the business when the agent can't finish (18). The MCP binding requires an idempotency-key UUID on checkout calls for retry safety (18). Official SDKs in Python and JavaScript; every request needs a UCP-Agent profile (13 of 15). 18 + 15 + 18 + 18 + 13 = 82.

ACK-Pay (Agent Commerce Kit) 77

ACK-Pay is a payment protocol with a 402 request and a verifiable receipt, but it names no settlement method of its own and no public Payment Service was found to pay through (25). Scored with the self-hosted rule for the rest. No protocol fee, with any conversion fee left to the Payment Service to disclose (20). Docs and SDK are MIT with nothing to buy (20). The SDK installs from npm with no account, but a payment needs a Payment Service and a Receipt Service that somebody has to run (12). 25 + 20 + 20 + 12 = 77.

Universal Commerce Protocol (UCP) 50

Protocol reading. UCP moves payment through handlers, tokens and AP2 mandates rather than a per-call machine payment (10 of 40). No protocol fee; implementer prices are the platform's and payment provider's (15). The spec, SDKs and samples are free (20). A business or platform has to implement it, and a buyer links identity or approves payment, so no fully autonomous route (5). 10 + 15 + 20 + 5 = 50.

ACK-Pay (Agent Commerce Kit) 43

0.11.0 of every package was tagged on 4 August 2026, 92 days before this check, and no tag has followed (10, in place of 20, cause time). No release from 6 August, and nine changesets wait on main, the newest from 23 September (0). GitHub's issue, pull request and Actions pages weren't readable on 4 November (the proxy answers 403); readings from them are per the 9 October check. 16 open issues, the oldest from 10 August 2026, and 37 open pull requests on 9 October; outside contributions were merged in September and on 6 October 2026, the last commit on main (15). One official SDK, current on npm (8). CI on every push, Dependabot and a scheduled daily audit workflow (10). 10 + 0 + 15 + 8 + 10 = 43.

Universal Commerce Protocol (UCP) 70

The latest release is v2026-08-25, 73 days before this check (20). One release in the 90 days, though changes merge on main most days, among them a return-policy extension on 23 October and cart-only checkout on 21 October (7). Pull requests from Google, Shopify and outside contributors merge within days; 262 issues and pull requests are open (18). Official SDKs, updated 5 November (15). CI with linting, spellcheck, governance checks and example validation, and Dependabot updates (10). 20 + 7 + 18 + 15 + 10 = 70.

ACK-Pay (Agent Commerce Kit) 66

The SDK exports Valibot and Zod schemas for the Payment Request, the payment option and the receipt claim, with no JSON Schema or OpenAPI file (15). llms.txt lists 42 pages on 4 November and each has a Markdown copy (10). Pages on roles, both sequences, the Payment Service and receipts explain when each flow applies, in descriptive prose without MUST or SHOULD rules (13). A field table gives type and required status for every request field, while network and recipient are free strings whose format varies by network (10). JSON examples of a request and a receipt are given, and no error responses are defined (7). Date-based protocol versions and a changelog per package, though the docs and SDK disagree in places. The docs allow a DID in serviceCallback and open issue 205 reports the schema rejects it (11). 15 + 10 + 13 + 10 + 7 + 11 = 66.

Universal Commerce Protocol (UCP) 90

OpenAPI for each REST service, OpenRPC for the MCP and embedded bindings and JSON Schema 2020-12 throughout (25). ucp.dev serves llms.txt, and AGENT_IMPLEMENTER.md guides agents implementing the spec (10). The spec gives MUST and SHOULD rules with rationale for negotiation, signatures and permalinks (17). Typed schemas with required fields, namespaced extension types and version requirements (13). Examples validated in CI and an error code table with continue_url handling (13). Dated versions with release tags and release-note drafts generated from tags; no separate changelog page was read (12). 25 + 10 + 17 + 13 + 13 + 12 = 90.

ACK-Pay (Agent Commerce Kit) 62

Docs and code are MIT, copyright Catena Labs, Inc. (30). No privacy policy or terms were found for agentcommercekit.com. The protocol pages say receipt metadata must not hold secrets or customer data and that the Payment Service hides the server's settlement account from the client (10). The versioning page defines Draft, Current and Final revisions, and the 0.11.0 changelog lists each removed API with its replacement (13). The ack-pay package depends on four workspace packages and valibot, and no telemetry was found in its manifest. The docs site names no legal entity, which appears only in the repository's LICENCE file and package manifests (10). 30 + 10 + 13 + 10 = 63.

Universal Commerce Protocol (UCP) 47

Apache-2.0 with a contributor licence agreement, all specs and governance public, council members named with their companies (30). ucp.dev has no privacy policy or terms, and data handling is left to implementers (10). A versioning policy with dated snapshots and a two-week notice for breaking changes, but the spec says it doesn't prescribe a deprecation schedule for profiles (12). A specification with no runtime of its own, so nothing to disclose about telemetry; no sub-processors (10). 30 + 10 + 12 + 10 = 62.