L402 vs Universal Commerce Protocol (UCP)

L402 97

L402 is a machine payment protocol (40). No protocol fee, the payer pays Lightning routing fees and the price arrives in the invoice (20). Free to implement, with MIT tools (20). A funded Lightning wallet is all an agent needs, no account, though getting a node or custodial wallet usually takes a person, and Nostr Wallet Connect support in l402sdk is unreleased (17).

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.

L402 65

A header grammar in section 5.3 and a 533-line macaroon spec that defines minting, verification and caveats byte by byte (18). No llms.txt found, but the repository has an agent spec that states the whole protocol in about 560 tokens (7). The 402-line spec uses RFC 2119 language and covers HTTP and gRPC flows (17). Fields and caveat formats are defined, with less detail on the invoice parameters (11). Examples of challenge and credential headers, and no error codes beyond the status codes (7). No version number on the spec and no changelog, only a backwards-compatibility section for the LSAT name (5).

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.

L402 55

Graded as a protocol on reference implementations (30), public servers (25), spec stability (25) and test suites (20). Lightning Labs ships Aperture (a Go reverse proxy), lnget (a Go client) and l402sdk (a Rust core with Python, Go and WASM bindings, whose changelog dates 0.2.0 to 29 October 2026 with no tag in the repository), and the spec still points to third-party JavaScript libraries (22). There's no facilitator role and no directory, and the named production users on l402.tech are still Lightning Labs' own Loop and Pool (8). A standalone RFC-style spec rewritten in March 2026 and unchanged since 20 March, while bLIP-0026 isn't merged in the bLIP repository (its newest commit is 17 July) and the maintainers work in their own repository (15). No test vectors in the spec, but Aperture has unit tests for tampered tokens and l402sdk runs a regtest suite against Aperture with LND and Core Lightning (10). 22+8+15+10 = 55.

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.

L402 47

Aperture v0.4.3 on 2 October 2026, a signed release on the 0.4 line that backports rate-limit fixes, 32 days before the check. v0.5.0 (25 March) is still the newest on main, so go install at latest doesn't get v0.4.3 (20). Two dated releases in the 90 days from 5 August, v0.4.3 and l402sdk 0.2.0 in its changelog (29 October, untagged), against the three the line asks for. The spec and lnget have no commit since 20 March (0). Per the 1 October check, Aperture has 31 open issues; issue replies weren't re-read, and Aperture merged 17 pull requests from 12 August to 30 October, including outside contributors' (12). lnget's last release is v1.1.0 from 20 March 2026 and l402sdk 0.2.0 isn't tagged (7). CI runs in Aperture, lnget and l402sdk and dependencies were updated in October, Aperture's on 15 October and l402sdk's on 28 October (8). 20+0+12+7+8 = 47.

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.

L402 61

A 402, a Lightning payment and a retry, after which the same token works for later calls until its caveats expire (21). Caveats can carry expiry, service tiers and capabilities, but there's one price per challenge and no negotiation of options (12). No error vocabulary, so a client sees 402 or 401 and nothing more specific (6). Paying twice is avoided by reusing the token, and replay limits come only from caveats and revocation (12). Released clients and servers are Go only, the multi-language SDK is unreleased and the JavaScript options are third-party (10).

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.

L402 58

The credential is a bearer macaroon plus preimage, and the spec says an intercepted one can be reused. Binding to an IP, TLS certificate or origin through caveats is optional (18). Caveats can narrow a token's expiry and scope before it's handed to another agent, lnget has --max-cost and --max-fee, and the spec says clients SHOULD enforce a maximum payment (15). Clients MUST check the invoice amount before paying, since a server can ask for any sum (10). Lightning payments leave a preimage as proof but no receipt header, and Aperture adds a dashboard and Prometheus metrics for operators (8). No SECURITY.md in Aperture or lnget and no advisories in OSV for either. Aperture's main branch bound MPP challenges to their resource on 7 October, after issue 272 reported unverified MPP receipts, but no release carries it (7). 18+15+10+8+7 = 58.

Universal Commerce Protocol (UCP) 67

OAuth 2.0 identity linking, RFC 9421 signatures for signed agents with key IDs bound to JWK thumbprints, and payment handlers with token exchange instead of raw card data (25 of 30). Checkout can hand back to the buyer through continue_url or an embedded checkout, and AP2 mandates record consent, but unattended completion is allowed by design (15 of 20). The permalink spec treats URL inputs as untrusted and requires server-side validation, but we found no guidance on product text reaching an agent (5 of 15). Order events go to business webhooks; we didn't read whether they are signed (8 of 15). SECURITY.md routes reports to Google's intake with a stated response time and GitHub advisories (14 of 20). 25 + 15 + 5 + 8 + 14 = 67.