Glossary
Plain-language definitions for Machine Commerce Attestation (MCA) and the terms that surround it in the agent economy. Each entry has its own link — share a specific definition by pointing at its heading.
Machine Commerce Attestation (MCA)
An open evidence standard for the agent economy. MCA attests who paid, under whose authority, and what was delivered — and makes checkpointed records independently verifiable with the open-source reference verifier.
Read the MCA overviewCommerce Triple
MCA's core primitive: a REQUEST, a PAYMENT, and a DELIVERY, each hashed and bound together into a single attestation record. MCA stores hashes and metadata only — the specification prohibits storing payload bodies.
Attestation Record
The signed record produced when a commerce triple is bound together and appended to an MCA log.
Checkpoint
A periodic, dual-signed summary of an MCA log — a Merkle root over a range of record IDs — published so any party can confirm the log hasn't been altered without reading every record in it.
Query the latest checkpointEvidence Layer
MCA's position in the stack: above payment rails (cards, ACH, x402, AP2) and below governance, risk, and dispute-resolution systems — giving all of them a shared, verifiable record of what actually happened.
Agent Economy
The emerging environment in which AI agents act, spend, and fulfill commitments on a person's or organization's behalf, across payment rails and services.
Reference Log
IONDRA's public reference-log endpoint. The specification doesn't require a single log — anyone can run one. A descriptor is not a health signal; without a non-empty latest checkpoint there are no checkpointed records for which to claim integrity.
View the log descriptorReference Verifier (mca-verify)
A dependency-free, open-source implementation that checks an MCA log's published checkpoints and hash chain for integrity. It can run against IONDRA's public endpoint or any other MCA-compliant log; no checkpoint means there is no checkpointed range to verify.
View mca-verify on GitHubConformance Vector
A test case used to check whether an MCA implementation correctly follows the specification. IONDRA publishes a repository test result against vendored reference-verifier vectors — see Trust & Security for its scope.
See conformance resultsAP2 (Agent Payments Protocol)
An open protocol from Google and partners for how AI agents initiate and authorize payments on a user's behalf. AP2 is a payment-and-mandate protocol; MCA is complementary — it attests what happened on top of AP2 or any other rail, rather than moving money itself.
AP2 specificationx402
An open, HTTP-native micropayment protocol built on the HTTP 402 status code, originally developed by Coinbase's developer platform. Like AP2, x402 is a payment rail; MCA sits above it as the evidence layer, attesting the resulting commerce triple rather than handling the payment.
x402 specificationWant the full picture? Read the MCA overview or the MCA FAQ.