Latest read
paperAgentic Settlement Protocol
Escrow for purchases an agent makes now and a human confirms later: authorize, capture, refund.
arXiv · Sep 2026
Rayudu Ramisetti · going deep on
When the buyer is a program.
Agentic commerce is a purchase where software does the finding, the asking and the paying. This is where I keep what is worth reading, and what each protocol actually does — kept current, every link checked.
ACPCheckoutUCPCheckoutAP2Paymentx402PaymentMCPTransportA2ATransportRESTCheckout
Start here
Three reads, in order, if this is all new.
Reading list
- A Formal Analysis of Agent Payment ProtocolsarXiv · Aug 2026 · paper
- Protocol-Level Attacks on Agentic Commerce PlatformsarXiv · Jul 2026 · paper
- Model Context Protocol, 2026-07-28MCP · Jul 2026 · spec
- Web Bot AuthCloudflare · Jul 2026 · docs
The protocol map
Full comparison →- ACP Let an agent complete a purchase against a merchant that it does not have an account with.Checkout
- UCP The same job as ACP, with capability discovery first and more than one transport.Checkout
- AP2 Prove that a human authorised what the agent is about to buy.Payment
- x402 Charge for a single HTTP request, with no account and no checkout page.Payment
- MCP Give a model tools and data, including a merchant's catalogue and cart.Transport
- A2A Let two agents talk — a shopper's agent and a merchant's, for example.Transport
- REST The baseline.Checkout
Two status codes
402 or 403?
Most sites answer an agent with 403 Forbidden. Several household-name announcement pages refused a plain fetch while this reading list was being checked, so they could not be cited at all.
402 Payment Required is the other road: answer with terms a machine can act on, and get paid instead of ignored.
Why it matters →Four layers
Read any spec by asking which of these it answers.
- 1. DiscoveryCan an agent find and understand the product?
- 2. CheckoutCan it get a firm price and place the order?
- 3. PaymentCan money move, with limits?
- 4. Identity & trustDoes the merchant know who is calling, and on whose behalf?
Explainers
All 10 →Written by a human
I am building in this space and writing as I go. If you are working on it too, I would like to hear from you.