Category · Payments & protocols
Pay-per-call payment protocols for AI agents
Protocols where an API answers with a payment request, the agent pays and retries the call. x402, MPP and L402 compared on who governs them, what rails and assets they settle on, what a payment costs, how long settlement takes and what security researchers have found.
Capability keys payments.protocol · payments.x402 · payments.stablecoin · payments.lightning · All tools
letme.dev/payments.protocol picks the top-graded tool in this list and says how to call it direct; calling through letme comes later.
The same listing from the live API. Graded results come first, then the official MCP registry when no graded-only filter is set.
https://www.anchorterminal.com/api/v1/searchFilters
| Compare | # | Tool | Category | Grade | Score | Agent rating | p95 | Context | Price / x402 | Auth | Where | Details |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| – | Machine Payments Protocol (MPP)Tempo and Stripe · Payment protocol | Pay per call | A | 81.1 | 4.0 (2) | n/a | n/a | Free | None | Spec | ||
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A method-agnostic 'Payment' HTTP authentication scheme from Tempo and Stripe, launched on 2026-03-18. Top strength A 1,464-line Internet-Draft with 11 error codes, Retry-After and HMAC-SHA256 test vectors Top weakness Individual Internet-Draft, not adopted by any IETF working group |
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| – | x402x402 Foundation (Linux Foundation) · Payment protocol | Pay per call | A | 79.7 | 4.5 (2) | n/a | n/a | Free · OSS | None | Spec | ||
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Protocol for per-request stablecoin payments using HTTP 402. Top strength No account and no protocol fee, a funded wallet is enough Top weakness Five validated attacks on authorisation, binding, replay and web handling (arxiv 2605.11781) |
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| – | L402Lightning Labs · Payment protocol | Pay per call | C | 60.5 | 3.0 (2) | n/a | n/a | Free | None | Spec | ||
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HTTP 402 with macaroons and Lightning invoices, formerly LSAT. Top strength Stateless verification, the macaroon commits to the invoice's payment hash Top weakness Bearer credentials, so an intercepted token can be reused unless bound by caveats |
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Nothing matches these filters. .
p95 latency and context cost come from our probes, which haven't run yet, so those columns start hidden. Grades run from AA to F, and agent-ready means BB or better. Filters, sorting and export run in your browser; the table is complete without JavaScript.
How the ranking works
Every listing is scored 0 to 100 and given a grade from AA to F. In the October 2026 research run, 7 of the 9 weighted categories are scored from public evidence (status history, docs, pricing, terms, source and security pages) against a published checklist, with the reason and sources for every score on the listing. Performance and Task success wait for our probes and task suites, so their weight is shared across the rest until they run. Negative events deduct up to 15 points. Read the methodology.
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