What does Not documented mean?

Not documented means the page checked for that cell does not state the fact. The cell still links that page and the day it was read.

Does a shared layer mean two protocols interoperate?

No. A shared layer says where each one sits. Composition is a separate column, and it is filled only when a cited page says one references or carries the other.

Where is the machine readable matrix?

GET /data/protocol-compatibility.json. The file includes every row, the cited sources, and the as of dates. The HTML table includes the same rows.

Does the layer filter hide rows?

No. Layer links add a mark. Every row stays in the server rendered table.

Tool

Protocol compatibility

This matrix records layer, settlement, and composition for directory protocols and payment rails, plus four identity protocols. Each filled cell cites the page that states the fact and the day that page was read. If the page does not state the fact, the cell says Not documented. Rows are alphabetical. The full table stays in the HTML.

Last verified 2026-10-21

Takeaways

These rows do not sit on one layer. MCP's specification describes tools, resources, and prompts. The A2A site describes agent to agent messaging. ACP and UCP describe checkout. x402, L402, and MPP describe HTTP payment.
AP2's site calls it an extension for A2A and UCP, and it links an x402 sample. The A2A x402 extension spec describes nesting x402 data inside an AP2 mandate.
- AP2 protocol documentation
- A2A x402 payments extension v0.2
The UCP specification defines REST, MCP, and A2A transports, and it describes AP2 mandate signing and optional Web Bot Auth key lookup.
- Universal Commerce Protocol specification
Visa's specification says its agent signature is aligned with web-bot-auth. The ACP repository checked on 2026-10-21 does not say that ACP implements UCP.
- Visa Trusted Agent Protocol specifications
- Agentic Commerce Protocol repository
A settlement asset is filled only when the cited page names it. x402.org says stablecoins are the primary use case. L402 binds the token to a Lightning invoice. AP2's site says the initial version supports credit and debit cards.

Protocol compatibility JSON · How x402 volume is measured

3 of 27 rows include Agent to agent messaging. The table below still lists every row. Matching rows are marked.

A2A
Agent Network Protocol
AGNTCY

Protocol compatibility, alphabetical by name
Name	Layer	Settlement	Composes with	License and governance	Status	Comparisons
A2A Marked for this layer	Agent to agent messaging. The project site says A2A is how independent agents discover each other, delegate tasks, and share results. A2A protocol site As of 2026-10-21	Not documented The project site read on 2026-10-21 does not name a settlement asset. A2A protocol site As of 2026-10-21	The project site says MCP connects an agent to tools and A2A connects agents to other agents, and that the two are meant to be used together. A2A protocol site As of 2026-10-21 AP2's site says the protocol is available as an extension for A2A and for the Universal Commerce Protocol. AP2 protocol documentation As of 2026-10-21 The UCP specification defines an A2A transport whose endpoint is an Agent Card URL. Universal Commerce Protocol specification As of 2026-10-21 The A2A x402 extension v0.2 spec defines on-chain payments for A2A, including an embedded flow that nests x402 data inside an AP2 mandate. A2A x402 payments extension v0.2 As of 2026-10-21 The PACT overview says the protocol sits on A2A 1.0. PACT protocol overview As of 2026-10-16 ERC-8004 names A2A as an agent communication protocol and allows a registration file to list an A2A endpoint. ERC-8004 Trustless Agents As of 2026-10-21	The project site says A2A was developed by Google, donated to the Linux Foundation, and is maintained by a Technical Steering Committee. A2A protocol site As of 2026-10-21 Apache-2.0. The same page states the Apache License 2.0. The GitHub license API also reported Apache-2.0 for a2aproject/A2A on 2026-10-21. A2A protocol site As of 2026-10-21	Live. The project site presents A2A as a published open standard. A2A protocol site As of 2026-10-21	A2A vs AGNTCY A2A vs Agent Network Protocol A2A vs Model Context Protocol
Agent Network Protocol Marked for this layer	Identity and auth. The README marks DID authentication, the did:wba method, and discovery as released v1.2. ANP specification index As of 2026-10-21 Agent to agent messaging. The README includes a messaging profile in the 1.2 set. Group end to end encryption remains a candidate. ANP specification index As of 2026-10-21	Not documented ANP-10 is listed as an AP2 payment adaptation draft and is not a released settlement rail. No current asset is named. ANP specification index As of 2026-10-21	The README lists ANP-10 as an AP2 payment adaptation draft, marked draft and not released. ANP specification index As of 2026-10-21	License notices on the README identify ANP Community. No separate standards body is named there. ANP specification index As of 2026-10-21 Apache-2.0. The README points at the repository LICENSE file. ANP specification index As of 2026-10-21	Spec set 1.2 is released for the core identity and discovery documents. Authorization, the meta-protocol, and the payment adaptation are marked draft. ANP specification index As of 2026-10-21	A2A vs Agent Network Protocol
Agent Vault	Checkout and commerce. A proxy checks the account holder's rules, then types the real value into the merchant page. How Agent Vault checkout works As of 2026-10-20 Identity and auth. The product gives an agent mock card and login tokens. The agent does not hold the card number. What is Agent Vault As of 2026-10-20	Card. The checked pages describe a mock card and a real card value typed into the merchant page. How Agent Vault checkout works As of 2026-10-20	Not documented The checked Agent Vault pages do not name another protocol in this directory. What is Agent Vault As of 2026-10-20	Self Labs publishes the product. What is Agent Vault As of 2026-10-20 Not documented The listing has no public repository. The checked page does not name a license. What is Agent Vault As of 2026-10-20	Directory status: live. The directory classified the listing as live when those pages were checked. What is Agent Vault As of 2026-10-20	None in this directory.
Agentic Commerce Protocol	Checkout and commerce. Stripe's documentation says ACP defines checkout sessions, cart and feed, delegated payment, orders, and webhooks. Stripe documentation for the Agentic Commerce Protocol As of 2026-10-21 Identity and auth. The same page says delegated authentication uses OAuth 2.0 so an agent can act for a buyer with a business. Stripe documentation for the Agentic Commerce Protocol As of 2026-10-21	Not documented The page describes delegated payment tokens and does not fix one settlement asset. The getting started guide says payment flows to the merchant. Stripe documentation for the Agentic Commerce Protocol As of 2026-10-21	Not documented The repository README and the Stripe ACP page checked on 2026-10-21 do not say ACP implements UCP, MCP, A2A, AP2, or x402. Agentic Commerce Protocol repository As of 2026-10-21	The repository says OpenAI and Stripe are the founding maintainers. Agentic Commerce Protocol repository As of 2026-10-21 Stripe's documentation says the protocol was created by Stripe, OpenAI, and Meta. Stripe documentation for the Agentic Commerce Protocol As of 2026-10-21 Apache-2.0. The repository README states the Apache 2.0 License. The GitHub license API reported Apache-2.0 on 2026-10-21. Agentic Commerce Protocol repository As of 2026-10-21	Beta. The repository README says the specification is currently in beta. Agentic Commerce Protocol repository As of 2026-10-21	Agentic Commerce Protocol vs Universal Commerce Protocol
AGNTCY Marked for this layer	Identity and auth. The project is described as an open stack for cross vendor agent discovery and identity. AGNTCY project site As of 2026-10-20 Agent to agent messaging. The same description includes messaging and observability. AGNTCY project site As of 2026-10-20	Not documented The project description checked for the listing does not name a settlement asset. AGNTCY project site As of 2026-10-20	Not documented The Linux Foundation welcome and the project site used for the listing do not name another protocol in this directory. Linux Foundation welcome of the AGNTCY project As of 2026-10-20	The Linux Foundation welcomed the project. Linux Foundation welcome of the AGNTCY project As of 2026-10-20 Apache-2.0. The GitHub license API reported this SPDX identifier on 2026-10-21. GitHub repository agntcy/dir As of 2026-10-21	Directory status: live. The directory classified the listing as live when the project site was checked. AGNTCY project site As of 2026-10-20	A2A vs AGNTCY
AP2	Checkout and commerce. A checkout mandate captures the cart negotiated between an agent and a merchant. AP2 protocol documentation As of 2026-10-21 Payment settlement. A payment mandate authorizes payment against a payment instrument. AP2 protocol documentation As of 2026-10-21	Credit and debit cards in the initial version. The page calls these common pull payment methods. AP2 protocol documentation As of 2026-10-21 Not documented Stablecoin, Lightning, and bank are not named as current rails. The same page puts real time bank transfers and digital currencies on a roadmap. AP2 protocol documentation As of 2026-10-21	The site says AP2 is an extension for A2A and for the Universal Commerce Protocol. AP2 protocol documentation As of 2026-10-21 The same page also calls AP2 an open extension for A2A and MCP. AP2 protocol documentation As of 2026-10-21 The site links a human not present sample that uses x402. AP2 protocol documentation As of 2026-10-21 The A2A x402 extension v0.2 spec describes an embedded flow that places x402 payment data inside an AP2 cart mandate and payment mandate. A2A x402 payments extension v0.2 As of 2026-10-21	The site says standardization continues in the FIDO Alliance Agentic Authentication and Payments technical working groups. The public repository hosts the current specification. AP2 protocol documentation As of 2026-10-21 Apache-2.0. The GitHub license API reported this SPDX identifier on 2026-10-21. GitHub repository google-agentic-commerce/AP2 As of 2026-10-21	Directory status: beta. The site documents public samples and says FIDO continues the standards work. AP2 protocol documentation As of 2026-10-21	AP2 vs Machine Payments Protocol
Coinbase Agentic Wallet	Payment settlement. The documentation describes a wallet the agent uses to hold USDC, send, trade, and pay for services. Coinbase Agentic Wallet documentation overview As of 2026-10-19	Stablecoin. The listing source says the agent holds USDC. Coinbase Agentic Wallet documentation overview As of 2026-10-19	The listing source says the agent pays x402 services. Coinbase Agentic Wallet documentation overview As of 2026-10-19 The same source says the MCP version is labeled beta. Coinbase Agentic Wallet documentation overview As of 2026-10-19	Coinbase Developer Platform publishes the wallet. Coinbase Agentic Wallet documentation overview As of 2026-10-19 Not documented The listing has no public repository. The checked page does not name a license. Coinbase Agentic Wallet documentation overview As of 2026-10-19	Directory status: live. The listing source says the MCP version is labeled beta. Coinbase Agentic Wallet documentation overview As of 2026-10-19	None in this directory.
ERC-8004	Identity and auth. The EIP specifies an ERC-721 identity registry, a reputation registry, and a validation registry. ERC-8004 Trustless Agents As of 2026-10-21	Not documented The EIP says payments are orthogonal to this protocol and are not covered. It does not name a settlement asset. ERC-8004 Trustless Agents As of 2026-10-21	The motivation names MCP for tools and A2A for agent messaging, and says those protocols do not cover discovery and trust. ERC-8004 Trustless Agents As of 2026-10-21 A registration file may list A2A and MCP endpoints. ERC-8004 Trustless Agents As of 2026-10-21 The EIP says examples show how x402 payments can enrich feedback signals. Payments are not part of the protocol. ERC-8004 Trustless Agents As of 2026-10-21	Ethereum Improvement Proposal. The page lists the authors and the discussion thread. ERC-8004 Trustless Agents As of 2026-10-21 CC0. The EIP says copyright and related rights are waived via CC0. ERC-8004 Trustless Agents As of 2026-10-21	Draft. The EIP page labels the proposal Draft. ERC-8004 Trustless Agents As of 2026-10-21	Microsoft Entra Agent ID vs ERC-8004
Hedera Agent Accounts	Payment settlement. The announcement describes an owner funded spending account with a daily cap, a per transaction maximum, and a recipient allowlist. Introducing Hedera Agent Accounts As of 2026-10-19	Not documented The announcement does not name stablecoin, card, Lightning, or bank as the settlement asset. Introducing Hedera Agent Accounts As of 2026-10-19	Not documented The announcement does not name another protocol in this directory. Introducing Hedera Agent Accounts As of 2026-10-19	Hedera publishes the announcement. Introducing Hedera Agent Accounts As of 2026-10-19 Not documented The listing has no public repository. The announcement does not name a license. Introducing Hedera Agent Accounts As of 2026-10-19	Spec. The announcement says public testnet access is still forthcoming. Introducing Hedera Agent Accounts As of 2026-10-19	None in this directory.
L402	Payment settlement. The server answers HTTP 402 with a token bound to a Lightning invoice. The client pays, then presents the preimage. Lightning Labs L402 documentation As of 2026-10-21	Lightning. The token commits to a Lightning invoice by its payment hash. Lightning Labs L402 documentation As of 2026-10-21	Not documented The L402 page read on 2026-10-21 does not name x402, MPP, AP2, or another protocol in this directory. Lightning Labs L402 documentation As of 2026-10-21	Lightning Labs publishes the L402 documentation. Aperture is described there as an implementation. Lightning Labs L402 documentation As of 2026-10-21 Not documented The L402 documentation page does not state a license for the protocol text. Lightning Labs L402 documentation As of 2026-10-21 MIT for the Aperture repository, which the L402 page calls an implementation. The GitHub license API reported this SPDX identifier on 2026-10-21. GitHub repository lightninglabs/aperture As of 2026-10-21	Live. The documentation presents L402 as the current standard for this HTTP 402 flow. Lightning Labs L402 documentation As of 2026-10-21	L402 vs x402
Machine Payments Protocol	Payment settlement. The MPP site calls it an open standard for machine to machine payments via HTTP 402. MPP protocol site As of 2026-10-21	The MPP documentation index describes stablecoin, card, and Lightning Bitcoin payment methods. MPP protocol site As of 2026-10-21 Stripe's documentation describes authorization with a card or a stablecoin. Stripe documentation for MPP As of 2026-10-16	The MPP documentation index includes a guide for using MPP with x402. MPP protocol site As of 2026-10-21 The same index describes an MCP and JSON-RPC transport for MPP challenges. MPP protocol site As of 2026-10-21	Stripe's documentation describes MPP as co-authored by Stripe and Tempo. Stripe documentation for MPP As of 2026-10-16 Apache-2.0. The GitHub license API reported this SPDX identifier on 2026-10-21. GitHub repository tempoxyz/mpp As of 2026-10-21	Live. The MPP site presents the protocol as an open standard. MPP protocol site As of 2026-10-21	AP2 vs Machine Payments Protocol Machine Payments Protocol vs x402
Mastercard Agent Pay for Machines	Payment settlement. The 2026-10-20 article says an agent signs a payment voucher after an HTTP 402 response, inside a spending limit. Mastercard Agent Pay for Machines at Cloudflare Connect, 2026-10-20 As of 2026-10-21	The article says settlement in the demonstration can be fiat or stablecoins, and that on-chain settlement uses Base. Vouchers can be redeemed later. Mastercard Agent Pay for Machines at Cloudflare Connect, 2026-10-20 As of 2026-10-21	The article says Agent Pay for Machines builds on x402. Mastercard Agent Pay for Machines at Cloudflare Connect, 2026-10-20 As of 2026-10-21	Mastercard publishes the protocol. Mastercard Agent Pay for Machines at Cloudflare Connect, 2026-10-20 As of 2026-10-21 Not documented The article does not name a license. The listing has no public repository. Mastercard Agent Pay for Machines at Cloudflare Connect, 2026-10-20 As of 2026-10-21	Beta. The article dated 2026-10-20 announces Early Access after pilots. Mastercard Agent Pay for Machines at Cloudflare Connect, 2026-10-20 As of 2026-10-21	None in this directory.
MetaMask Agent Wallet	Payment settlement. The documentation describes a wallet CLI for sending tokens and paying requests. MetaMask Agent Wallet trading modes As of 2026-10-19	Not documented The checked page says the wallet sends tokens. It does not name stablecoin, card, Lightning, or bank. MetaMask Agent Wallet trading modes As of 2026-10-19	The listing source says the CLI pays x402 requests. MetaMask Agent Wallet trading modes As of 2026-10-19	MetaMask publishes the documentation. MetaMask Agent Wallet trading modes As of 2026-10-19 Not documented The listing has no public repository. The checked page does not name a license. MetaMask Agent Wallet trading modes As of 2026-10-19	Directory status: live. The directory classified the listing as live when the page was checked. MetaMask Agent Wallet trading modes As of 2026-10-19	None in this directory.
Model Context Protocol	Tool access. The specification says servers can offer resources, prompts, and tools to a client. Model Context Protocol specification As of 2026-10-21	Not documented The specification read on 2026-10-21 does not name a settlement asset. Model Context Protocol specification As of 2026-10-21	The A2A project site says MCP is the tool interface and A2A is the agent to agent interface. A2A protocol site As of 2026-10-21 The UCP specification defines an MCP transport. Universal Commerce Protocol specification As of 2026-10-21 The Personal Agent Protocol draft says a company publishes how an agent may act using OAuth, OpenAPI, and MCP. Personal Agent Protocol draft specification As of 2026-10-16 ERC-8004 names MCP and allows a registration file to list an MCP endpoint. ERC-8004 Trustless Agents As of 2026-10-21 The MPP documentation index describes an MCP transport for payment challenges. MPP protocol site As of 2026-10-21 AP2's site calls AP2 an open extension for A2A and MCP. AP2 protocol documentation As of 2026-10-21	GOVERNANCE.md says Model Context Protocol is a series of LF Projects, LLC. Model Context Protocol governance As of 2026-10-21 New code and specifications are Apache-2.0. Documentation other than specifications is CC-BY-4.0. Some earlier contributions remain under MIT until the author agrees to relicense. Model Context Protocol LICENSE As of 2026-10-21	Live. The specification dated 2026-07-28 is the published specification linked from the project. Model Context Protocol specification As of 2026-10-21	A2A vs Model Context Protocol
Nevermined	Payment settlement. The documentation describes a facilitator that verifies and settles charges against a payment plan. Nevermined payments facilitator As of 2026-10-21	Card, through delegated card spending. The page also says it settles x402 and MPP charges and does not name the asset inside those charges. Nevermined payments facilitator As of 2026-10-21	The page says the facilitator verifies and settles x402 and MPP charges. Nevermined payments facilitator As of 2026-10-21	Nevermined publishes the facilitator. Nevermined payments facilitator As of 2026-10-21 Not documented The listing has no public repository. The checked page does not name a license. Nevermined payments facilitator As of 2026-10-21	Directory status: live. The directory classified the listing as live when the page was checked. Nevermined payments facilitator As of 2026-10-21	None in this directory.
PACT	Identity and auth. A personal agent signs requests and acts for a user only inside scopes that user approved with a brand. PACT protocol overview As of 2026-10-16	Not documented The overview used for the listing does not name a settlement asset. PACT protocol overview As of 2026-10-16	The overview says the protocol sits on A2A 1.0. PACT protocol overview As of 2026-10-16	Not documented The overview used for the listing does not name a standards body. PACT protocol overview As of 2026-10-16 Apache-2.0. The GitHub license API reported this SPDX identifier on 2026-10-21. GitHub repository openpactprotocol/openpactprotocol As of 2026-10-21	Directory status: beta. The directory classified the listing as beta when the overview was checked. PACT protocol overview As of 2026-10-16	PACT vs Personal Agent Protocol
Personal Agent Protocol	Identity and auth. The draft describes how a company publishes the way a personal agent may sign in and act on a person's account. Personal Agent Protocol draft specification As of 2026-10-16	Not documented The draft used for the listing does not name a settlement asset. Personal Agent Protocol draft specification As of 2026-10-16	The draft uses OAuth, OpenAPI, and MCP. Personal Agent Protocol overview As of 2026-10-16	Not documented The draft used for the listing does not name a standards body. Personal Agent Protocol draft specification As of 2026-10-16 Apache-2.0. The GitHub license API reported this SPDX identifier on 2026-10-21. GitHub repository personal-agent-protocol/personal-agent-protocol As of 2026-10-21	Spec. The linked document is a draft specification at version 0.2. Directory status: designed. Personal Agent Protocol draft specification As of 2026-10-16	PACT vs Personal Agent Protocol
Polygon Agent CLI	Payment settlement. The CLI reference describes an embedded smart wallet and session spending inside an owner approved allowance. Polygon Agent CLI reference As of 2026-10-19	Not documented The reference describes an allowance and per call caps. It does not name stablecoin, card, Lightning, or bank. Polygon Agent CLI reference As of 2026-10-19	The listing source says x402 payments can be capped per call. Polygon Agent CLI reference As of 2026-10-19	Polygon publishes the CLI reference. Polygon Agent CLI reference As of 2026-10-19 MIT. The GitHub license API reported this SPDX identifier on 2026-10-21. GitHub repository 0xPolygon/polygon-agent-cli As of 2026-10-21	Directory status: live. The directory classified the listing as live when the reference was checked. Polygon Agent CLI reference As of 2026-10-19	None in this directory.
Skyfire	Identity and auth. KYAPay tokens bind an agent identity to a payment the buyer has committed. Skyfire KYAPay token documentation As of 2026-10-16 Payment settlement. The seller charges the committed payment after delivery. Skyfire payments and settlement As of 2026-10-16	Not documented The listing summary of the settlement page does not name stablecoin, card, Lightning, or bank. Skyfire payments and settlement As of 2026-10-16	Not documented The checked Skyfire pages do not name another protocol in this directory. Skyfire KYAPay token documentation As of 2026-10-16	Skyfire publishes the documentation. Skyfire KYAPay token documentation As of 2026-10-16 Not documented The listing has no public repository. The checked page does not name a license. Skyfire KYAPay token documentation As of 2026-10-16	Directory status: live. The directory classified the listing as live when the page was checked. Skyfire KYAPay token documentation As of 2026-10-16	Skyfire vs Tempo Wallet
Stripe link-cli	Checkout and commerce. The documentation describes an agent requesting a card purchase. Enable agents to spend As of 2026-10-19 Payment settlement. Link asks the customer to approve the spend, then returns a one time payment credential. Enable agents to spend As of 2026-10-19	Card. The listing source also says the CLI can request a Machine Payments Protocol charge. stripe/link-cli README As of 2026-10-19	The README says the CLI can request a Machine Payments Protocol charge. stripe/link-cli README As of 2026-10-19	Stripe publishes the CLI. stripe/link-cli README As of 2026-10-19 MIT. The GitHub license API reported this SPDX identifier on 2026-10-21. GitHub repository stripe/link-cli As of 2026-10-21	Directory status: live. The directory classified the listing as live when the README was checked. stripe/link-cli README As of 2026-10-19	None in this directory.
Sui Agentic Payments	Payment settlement. The page describes a testnet gateway where an agent pays per API call. Sui Agent Payments As of 2026-10-19	Stablecoin. The page says payment is in USDC on Sui. Sui Agent Payments As of 2026-10-19	Not documented The page does not name x402, MPP, or another protocol in this directory. Sui Agent Payments As of 2026-10-19	Sui publishes the page. Sui Agent Payments As of 2026-10-19 Not documented The listing has no public repository. The page does not name a license. Sui Agent Payments As of 2026-10-19	Beta. The page describes a testnet gateway. Directory status: beta. Sui Agent Payments As of 2026-10-19	None in this directory.
Tempo Wallet	Payment settlement. The documentation describes a wallet and CLI that preview payment terms and pay under a max spend cap. Tempo Wallet agent documentation As of 2026-10-19	Not documented The checked wallet pages name MPP terms and a spend cap. They do not name stablecoin, card, Lightning, or bank. Tempo Wallet agent documentation As of 2026-10-19	The listing source says the wallet previews MPP terms. Tempo guide to paying with the CLI As of 2026-10-19	Tempo publishes the wallet documentation. Tempo Wallet agent documentation As of 2026-10-19 Not documented The listing has no public repository. The checked page does not name a license. Tempo Wallet agent documentation As of 2026-10-19	Directory status: live. The directory classified the listing as live when the page was checked. Tempo Wallet agent documentation As of 2026-10-19	Skyfire vs Tempo Wallet
Universal Commerce Protocol	Checkout and commerce. The specification says businesses and platforms negotiate capabilities and payment handlers. Universal Commerce Protocol specification As of 2026-10-21 Identity and auth. The specification defines HTTP message signatures and public keys on the profile. Universal Commerce Protocol specification As of 2026-10-21	Not documented The specification separates payment instruments from payment handlers. It does not fix one settlement asset for the protocol. Universal Commerce Protocol specification As of 2026-10-21	The specification defines REST, MCP, and A2A transports. Universal Commerce Protocol specification As of 2026-10-21 The specification describes AP2 mandate signing and says a business that does not use AP2 may publish a single baseline key. Universal Commerce Protocol specification As of 2026-10-21 The specification defines optional Web Bot Auth interop, including a Signature-Agent header and the tag web-bot-auth. Universal Commerce Protocol specification As of 2026-10-21	The specification overview says reverse domain names encode governance authority and that this removes the need for a central registry. Universal Commerce Protocol specification As of 2026-10-21 Apache-2.0. Universal Commerce Protocol LICENSE As of 2026-10-21	Live. A current specification is published at the UCP specification URL. Universal Commerce Protocol specification As of 2026-10-21	Agentic Commerce Protocol vs Universal Commerce Protocol
Visa Trusted Agent Protocol	Identity and auth. Merchants verify an agent from an RFC 9421 HTTP message signature bound to the site and the action. Visa Developer Center: getting started with Trusted Agent Protocol As of 2026-10-21	Not documented The specification describes a payment container signature. It does not name a settlement asset for the protocol itself. Visa Trusted Agent Protocol specifications As of 2026-10-21	The specification says the agent recognition signature is based on RFC 9421 and aligned with web-bot-auth. Visa Trusted Agent Protocol specifications As of 2026-10-21	Visa publishes the specification. Visa Developer Center: getting started with Trusted Agent Protocol As of 2026-10-21 Not documented The listing source says the reference code is under Visa terms, not an open source license. This matrix did not read a LICENSE file in that repository on 2026-10-21. Trusted Agent Protocol reference code on GitHub As of 2026-10-21	The Visa press release dated July 2, 2026 reports live European merchant purchases through the protocol. Visa press release on live agentic transactions in Europe (Jul 2, 2026) As of 2026-10-21 A Visa developer use case page says the product is in development and deployment. Visa Trusted Agent Protocol use case As of 2026-10-21	Visa Trusted Agent Protocol vs Web Bot Auth
Web Bot Auth	Identity and auth. An automated client signs HTTP requests so a site can verify which bot or agent sent them. Cloudflare Web Bot Auth documentation As of 2026-10-19	Not documented The draft and the Cloudflare documentation used for the listing do not name a settlement asset. IETF webbotauth working group draft: HTTP Message Signatures for automated traffic As of 2026-10-19	Visa's Trusted Agent Protocol specification says its agent recognition signature is aligned with web-bot-auth. Visa Trusted Agent Protocol specifications As of 2026-10-21 The UCP specification defines optional Web Bot Auth interop for key lookup and signatures. Universal Commerce Protocol specification As of 2026-10-21	The signature rules are an IETF working group draft. IETF webbotauth working group draft: HTTP Message Signatures for automated traffic As of 2026-10-19 Apache-2.0 for the Cloudflare repository. The GitHub license API reported this SPDX identifier on 2026-10-21. GitHub repository cloudflare/web-bot-auth As of 2026-10-21 Not documented This cell does not state a separate license for the IETF draft text. IETF webbotauth working group draft: HTTP Message Signatures for automated traffic As of 2026-10-19	Draft. The IETF datatracker lists a working group draft. The directory lists the method as beta and says it is not yet a standard. IETF webbotauth working group draft: HTTP Message Signatures for automated traffic As of 2026-10-19	Microsoft Entra Agent ID vs Web Bot Auth Visa Trusted Agent Protocol vs Web Bot Auth
x401	Identity and auth. A server sends a proof request header for a verifiable credential, and the agent returns a proof response. x401 HTTP proof requirement protocol As of 2026-10-20	Not documented The listing summary says payment stays on HTTP 402. The checked summary does not name a settlement asset. x401 HTTP proof requirement protocol As of 2026-10-20	Not documented The listing summary separates this proof flow from payment and does not name the x402 protocol. x401 HTTP proof requirement protocol As of 2026-10-20	Proof publishes the specification. Proof developer guide to x401 As of 2026-10-20 Apache-2.0. The GitHub license API reported this SPDX identifier on 2026-10-21. GitHub repository proof/x401 As of 2026-10-21	Beta. The listing summary says the draft protocol is at version 0.2.0. Directory status: beta. x401 HTTP proof requirement protocol As of 2026-10-20	None in this directory.
x402	Payment settlement. A server answers with HTTP 402, the client pays and retries, and a facilitator can verify and settle the payment. x402 site As of 2026-10-21	The x402.org FAQ says stablecoin payments are the primary use case, and that the protocol is extensible to traditional payment methods. x402 site As of 2026-10-21 The same FAQ says x402 supports EVM compatible chains, Solana, and more. x402 site As of 2026-10-21 The Linux Foundation announcement says payment types range from traditional cards to stablecoins. Linux Foundation announcement of the x402 Foundation, 14 July 2026 As of 2026-10-21	The A2A x402 extension v0.2 spec defines an A2A extension for x402 payments, including an embedded flow inside AP2. A2A x402 payments extension v0.2 As of 2026-10-21 AP2's site links a human not present sample that uses x402. AP2 protocol documentation As of 2026-10-21 The MPP documentation index includes a guide for using MPP with x402. MPP protocol site As of 2026-10-21 Mastercard's 2026-10-20 article says Agent Pay for Machines builds on x402. Mastercard Agent Pay for Machines at Cloudflare Connect, 2026-10-20 As of 2026-10-21 ERC-8004 says examples show x402 payments enriching feedback, and that payments are outside the ERC. ERC-8004 Trustless Agents As of 2026-10-21	The Linux Foundation announcement on 14 July 2026 says Coinbase contributed the protocol and the x402 Foundation stewards it. Linux Foundation announcement of the x402 Foundation, 14 July 2026 As of 2026-10-21 Apache-2.0. The GitHub license API reported this SPDX identifier on 2026-10-21. GitHub repository x402-foundation/x402 As of 2026-10-21	Live. The x402.org FAQ says the protocol is production ready. x402 site As of 2026-10-21	L402 vs x402 Machine Payments Protocol vs x402

How this works

Rows are the protocol listings, the payment rail listings, and four identity protocols already in the directory: ERC-8004, Visa Trusted Agent Protocol, Web Bot Auth, and x401. The order is alphabetical by listing name.

A filled cell quotes a primary page and the day that page was read. Not documented means that page does not state the fact. It is not a claim that the fact is false.

A shared layer does not mean two rows interoperate. Composition is recorded only when the cited page says one references, extends, or carries the other.

The layer links are ordinary URLs. The table in the HTML always contains all 27 rows.

Questions

What does Not documented mean?: Not documented means the page checked for that cell does not state the fact. The cell still links that page and the day it was read.
Does a shared layer mean two protocols interoperate?: No. A shared layer says where each one sits. Composition is a separate column, and it is filled only when a cited page says one references or carries the other.
Where is the machine readable matrix?: GET /data/protocol-compatibility.json. The file includes every row, the cited sources, and the as of dates. The HTML table includes the same rows.
Does the layer filter hide rows?: No. Layer links add a mark. Every row stays in the server rendered table.

Sources

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