# The Agent Protocol Atlas

> The protocols of the agentic web (June 2026), grouped by the layer they operate at: how agents reach tools, talk to each other, prove who they are, transact, and consume content. This enriched edition adds full EAV depth per record — canonical spec source, governance, spec version + date, transport, core mechanism, discovery endpoint, adoption metric (sourced), relationship edges, and a per-record use/when-to-use/when-not-to-use decision triple plus a code example.
> Updated 2026-06-15. JSON: /api/protocols · single record: /api/protocols/{id}

## Discovery & Declaration — how a site announces itself to agents

### llms.txt — llms.txt (llms-txt)

- **Layer:** discovery
- **Creator:** Jeremy Howard (Answer.AI)
- **Status:** widely adopted (~10% of studied sites) (2024)
- **What:** A markdown file at the domain root that gives language models a curated map of a site's most important content.
- **Spec:** https://llmstxt.org
- **Source:** Origin proposal (Jeremy Howard, Answer.AI), 2024-09-03: https://www.answer.ai/posts/2024-09-03-llmstxt.html . Spec home: https://llmstxt.org .

```
# Site Name
> One-line description.
## Core
- [Page](/page.md): what it is
```

### NLWeb — Natural Language Web (nlweb)

- **Layer:** discovery
- **Creator:** Microsoft (R.V. Guha)
- **Status:** emerging (2025)
- **What:** Turns a website into a conversational, queryable endpoint by combining Schema.org data, a vector store and an LLM — and every NLWeb endpoint is also an MCP server.
- **Spec:** https://github.com/nlweb-ai/NLWeb
- **Source:** Project (Microsoft / R.V. Guha), built on schema.org, MCP-server duality: https://github.com/nlweb-ai/NLWeb ; seed triple research §2.

```
POST /ask  { "query": "..." } → grounded natural-language answer + structured sources
```

### agents.json — agents.json / Arazzo API manifests (agents-json)

- **Layer:** discovery
- **Creator:** open community (built on the OpenAPI Arazzo spec)
- **Status:** emerging (2025)
- **What:** A manifest that describes a site's APIs and workflows in a form agents can discover and execute, typically served from /.well-known/.
- **Spec:** https://github.com/wild-card-ai/agents-json
- **Source:** Spec/repo (built on OpenAPI Arazzo): https://github.com/wild-card-ai/agents-json ; agents.json/agents.txt listed among Layer-1 discovery additions in research §2.

```
GET /.well-known/agents.json → { "endpoints": [ ... ], "workflows": [ ... ] }
```

### agents.txt — agents.txt (agents-txt)

- **Layer:** discovery
- **Creator:** open community (multiple competing proposals; asturwebs reference among them)
- **Status:** draft (community proposal) (2025)
- **What:** A root-level file that declares a site's identity, terms of use for AI agents, service catalog and agentic endpoints in a machine-readable form.
- **Spec:** https://github.com/asturwebs/agents-txt
- **Source:** Reference variant (MIT, v2.0 draft, identity/permissions/services/endpoints, /agents.txt + /api/agents, IANA well-known pending, agent-manifest.txt rename of one variant): https://github.com/asturwebs/agents-txt . Seed triple (agents.txt discovers MCP): research §2. Honesty note: multiple competing agents.txt proposals exist.

```
GET /agents.txt → identity, permissions, services, agentic endpoints (with /api/agents JSON twin)
```

### DNS-AID — DNS-based Agent Identification and Discovery (dns-aid)

- **Layer:** discovery
- **Creator:** IETF draft (draft-mozleywilliams-dnsop-dnsaid), community reference implementation
- **Status:** draft (IETF Internet-Draft) (2025)
- **What:** Lets organizations publish and discover AI agents through standard DNS records — a naming convention over SVCB/TXT/TLSA records, signed with DNSSEC, with no new record types or servers.
- **Spec:** https://datatracker.ietf.org/doc/draft-mozleywilliams-dnsop-dnsaid/
- **Source:** IETF Internet-Draft (naming convention over SVCB/TXT/TLSA per RFC 9460/4033, DNS-SD, DNSSEC/DANE-signed): https://datatracker.ietf.org/doc/html/draft-mozleywilliams-dnsop-dnsaid-02 ; project site https://dns-aid.org/ ; reference impl https://github.com/dns-aid/dns-aid-core . Listed for addition in research §2.

```
_agent._tcp.example.com  IN SVCB ...   → DNS-SD discovery of an org's agent index (DNSSEC-signed)
```

### schema.org — Schema.org structured data vocabulary (for agents) (schema-org)

- **Layer:** discovery
- **Creator:** Schema.org founding sponsors (Google, Microsoft, Yahoo, Yandex)
- **Status:** active (the agentic-web data foundation) (2011)
- **What:** The shared structured-data vocabulary (JSON-LD) that gives agents machine-readable entities and relationships to read off a page — the noun layer the agentic web is built on.
- **Spec:** https://schema.org
- **Source:** Schema.org vocabulary as the agentic-web data foundation (v30.0 reported 2026-03-25), JSON-LD: https://schema.org and https://schema.org/docs/releases.html . Seed triple (NLWeb built_on schema.org): research §2. Honesty note: there is no distinct 'schema.org-for-agents' spec; this records the existing vocabulary applied to agentic use.

```
<script type="application/ld+json">{ "@context": "https://schema.org", "@type": "Product", "name": "..." }</script>
```

## Capability & Tooling — how agents invoke tools and data

### MCP — Model Context Protocol (mcp)

- **Layer:** capability
- **Creator:** Anthropic (now governed under the Linux Foundation's Agentic AI Foundation)
- **Status:** de facto standard (2024)
- **What:** The USB-C of agent tooling: a single JSON-RPC interface for connecting any agent to any tool, data source, or service.
- **Spec:** https://modelcontextprotocol.io
- **Source:** Spec version/date: https://modelcontextprotocol.io/specification/2025-11-25 (latest stable, 2025-11-25). Governance (AAIF hosts MCP): competitive-research-2026-06.md §2.

```
{ "jsonrpc": "2.0", "method": "tools/call", "params": { "name": "search", "arguments": { "q": "..." } } }
```

### WebMCP — Web Model Context Protocol (webmcp)

- **Layer:** capability
- **Creator:** W3C Web Machine Learning Community Group (engineers from Google & Microsoft)
- **Status:** draft (Chrome 146 DevTrial) (2026)
- **What:** MCP for the browser: a web page registers callable tools on document.modelContext so a visiting agent invokes functions instead of clicking pixels.
- **Spec:** https://webmachinelearning.github.io/webmcp/
- **Source:** Status, editors, API surface, draft dated 15 June 2026: https://webmachinelearning.github.io/webmcp/ (Draft Community Group Report; not a W3C Standard). Governance (W3C): brief §L2 + research §2.

```
await document.modelContext.registerTool({ name, description, inputSchema, execute })
```

### OASF — Open Agentic Schema Framework (oasf)

- **Layer:** capability
- **Creator:** AGNTCY project (originated at Cisco / Outshift)
- **Status:** active (Linux Foundation AGNTCY) (2025)
- **What:** A standardized schema for describing AI agents — their capabilities, metadata and relationships — so agents can be discovered and understood across platforms; the 'DNS for agents' within AGNTCY.
- **Spec:** https://docs.agntcy.org/oasf/open-agentic-schema-framework/
- **Source:** OASF as AGNTCY's standardized agent-capability schema ('DNS for agents'), Apache-2.0, Linux Foundation: https://docs.agntcy.org/oasf/open-agentic-schema-framework/ and https://github.com/agntcy/oasf . AGNTCY/LF context: https://www.linuxfoundation.org/press/linux-foundation-welcomes-the-agntcy-project-to-standardize-open-multi-agent-system-infrastructure-and-break-down-ai-agent-silos . Listed for addition in research §2.

```
An OASF record describes an agent's capabilities via attribute-based taxonomies for cross-platform discovery.
```

## Agent Interop & Transport — how agents talk to each other

### A2A — Agent2Agent Protocol (a2a)

- **Layer:** interop
- **Creator:** Google (now under the Linux Foundation)
- **Status:** production (150+ orgs) (2025)
- **What:** The leading standard for agent-to-agent coordination: agents publish an Agent Card describing their skills, then negotiate and delegate tasks to one another.
- **Spec:** https://a2a-protocol.org
- **Source:** A2A project / Linux Foundation announcements, 2025–2026 (org count per project communications).

```
GET /.well-known/agent.json → { "name": "...", "skills": [ ... ], "endpoints": { ... } }
```

### ACP — Agent Communication Protocol (acp)

- **Layer:** interop
- **Creator:** IBM / AGNTCY
- **Status:** emerging (2025)
- **What:** A REST-native alternative to A2A for teams that want inter-agent messaging over plain HTTP with minimal new machinery.
- **Spec:** https://agentcommunicationprotocol.dev
- **Source:** Spec home: https://agentcommunicationprotocol.dev . Maintainer (IBM/AGNTCY): research §2 (AGNTCY listed among protocols to add).

```
POST /agents/{id}/runs  { "input": [ ... ] }  // ordinary REST, no special transport
```

### AGNTCY — AGNTCY (Internet of Agents project) (agntcy)

- **Layer:** interop
- **Creator:** Cisco (Outshift), with LangChain and Galileo; now Linux Foundation
- **Status:** active (Linux Foundation, since 29 July 2025) (2025)
- **What:** A Linux Foundation project building open infrastructure for an 'Internet of Agents' — discovery (OASF), identity, messaging (SLIM) and observability — so agents from different vendors interoperate.
- **Spec:** https://agntcy.org/
- **Source:** Cisco-originated (March 2025, with LangChain + Galileo), joined Linux Foundation 29 July 2025, 75+ companies, components OASF + SLIM + identity + observability: https://www.linuxfoundation.org/press/linux-foundation-welcomes-the-agntcy-project-to-standardize-open-multi-agent-system-infrastructure-and-break-down-ai-agent-silos and https://agntcy.org/ . Listed for addition in research §2.

```
AGNTCY: Agent Discovery (OASF) + Agent Identity + Agent Messaging (SLIM) + Observability.
```

### SLIM — Secure Low-latency Interactive Messaging (slim)

- **Layer:** interop
- **Creator:** AGNTCY project (Cisco / Outshift); Linux Foundation
- **Status:** active (AGNTCY component) (2025)
- **What:** AGNTCY's secure, low-latency messaging substrate for agent-to-agent, human-in-the-loop and tool communication, designed for multi-modal exchange and quantum-safe security.
- **Spec:** https://docs.agntcy.org/
- **Source:** SLIM as AGNTCY's secure low-latency messaging component (agent/human/tool, multi-modal, quantum-safe): https://docs.agntcy.org/ ; AGNTCY/LF context https://www.linuxfoundation.org/press/linux-foundation-welcomes-the-agntcy-project-to-standardize-open-multi-agent-system-infrastructure-and-break-down-ai-agent-silos . Listed for addition in research §2.

```
SLIM carries agent ↔ agent / human / tool messages with low latency and quantum-safe security.
```

### ANP — Agent Network Protocol (anp)

- **Layer:** interop
- **Creator:** Agent Network Protocol open-source community
- **Status:** emerging (open source) (2025)
- **What:** An open protocol aiming to be the 'HTTP of the agent internet': decentralized DID-based identity, a meta-protocol negotiation layer, and JSON-LD agent descriptions so billions of agents can connect.
- **Spec:** https://agent-network-protocol.com/
- **Source:** ANP three-layer architecture (did:wba identity, meta-protocol negotiation, JSON-LD agent description): https://agent-network-protocol.com/ and https://agent-network-protocol.com/specs/agent-description.html ; repo https://github.com/agent-network-protocol/AgentNetworkProtocol . Compared with MCP/ACP/A2A in arXiv:2505.02279. Listed for addition in research §2.

```
did:wba identity + meta-protocol negotiation + JSON-LD agent description for open agent discovery.
```

## Identity, Trust & Verification — how an agent proves who it is

### Web Bot Auth — Web Bot Authentication (HTTP Message Signatures) (web-bot-auth)

- **Layer:** identity
- **Creator:** IETF drafts, championed by Cloudflare
- **Status:** emerging (2025)
- **What:** Cryptographically proves which agent is making a request via HTTP Message Signatures — because a User-Agent string can be forged and a signature cannot.
- **Spec:** https://datatracker.ietf.org/doc/draft-meunier-web-bot-auth-architecture/
- **Source:** RFC 9421 + Ed25519 + Signature-Agent header + /.well-known/http-message-signatures-directory: https://datatracker.ietf.org/doc/html/draft-meunier-web-bot-auth-architecture-02 ; Cloudflare reference: https://http-message-signatures-example.research.cloudflare.com/ ; research §1.

```
Signature-Agent: "https://my-agent.example"
Signature-Input: sig1=("@authority" "signature-agent");keyid="..."
```

### ERC-8004 — ERC-8004: Trustless Agents (erc-8004)

- **Layer:** identity
- **Creator:** Marco De Rossi, Davide Crapis, Jordan Ellis, Erik Reppel (Ethereum Improvement Proposal)
- **Status:** Draft (Standards Track: ERC) (2025)
- **What:** An Ethereum standard adding on-chain Identity, Reputation and Validation registries so agents can be discovered and trusted across organizational boundaries — a trust layer that extends A2A.
- **Spec:** https://eips.ethereum.org/EIPS/eip-8004
- **Source:** Canonical EIP (Status: Draft; Created 2025-08-13; three registries Identity/Reputation/Validation; complements A2A and MCP): https://eips.ethereum.org/EIPS/eip-8004 . Authors: Marco De Rossi, Davide Crapis, Jordan Ellis, Erik Reppel. Seed triple (ERC-8004 provides identity for A2A): research §2.

```
Three on-chain registries — Identity, Reputation, Validation — give A2A agents portable, verifiable trust.
```

## Payments & Settlement — how agents authorize and move value

### x402 — HTTP 402 Payments (x402)

- **Layer:** payments
- **Creator:** Coinbase + web3 ecosystem partners
- **Status:** live (165M+ transactions by Apr 2026) (2025)
- **What:** Revives the dormant HTTP 402 status code so an agent can pay for a resource inline — request, get 402 with terms, pay in stablecoin, retry.
- **Spec:** https://x402.org
- **Source:** x402 facilitator / ecosystem reporting (x402.org), 2026. Volume figures are ecosystem-reported, not independently audited.

```
HTTP/1.1 402 Payment Required
{ "accepts": [{ "scheme": "exact", "maxAmountRequired": "$0.01", "payTo": "0x..." }] }
```

### AP2 — Agent Payments Protocol (ap2)

- **Layer:** payments
- **Creator:** Google (with 60+ payments & finance orgs)
- **Status:** emerging (2025)
- **What:** Payment-agnostic settlement inside the A2A task lifecycle — handles cards, bank transfers and crypto through one mandate-based framework.
- **Spec:** https://ap2-protocol.org
- **Source:** Launch 2025-09-16 + 60+ partners + three-mandate (Intent/Cart/Payment) VC design: https://cloud.google.com/blog/products/ai-machine-learning/announcing-agents-to-payments-ap2-protocol .

```
An agent presents a signed mandate; AP2 routes it to cards, ACH, or crypto rails.
```

### ACP (Agentic Commerce) — Agentic Commerce Protocol (acp-commerce)

- **Layer:** payments
- **Creator:** OpenAI + Stripe
- **Status:** live (ChatGPT Instant Checkout) (2025)
- **What:** Lets an agent complete a purchase inside the conversation — the checkout that powers ChatGPT's Instant Checkout.
- **Spec:** https://www.agenticcommerce.dev
- **Source:** Launch 2025-09-29 under Apache-2.0, four-actor contract, ChatGPT Instant Checkout: https://github.com/agentic-commerce-protocol/agentic-commerce-protocol (OpenAI + Stripe).

```
Agent submits a delegated payment token; merchant confirms the order over the protocol.
```

### UCP — Universal Commerce Protocol (ucp)

- **Layer:** payments
- **Creator:** Universal-Commerce-Protocol project (open standard; ucp.dev)
- **Status:** active (open standard) (2026)
- **What:** An open standard for interoperability between commerce entities so AI agents can discover products, fill carts, and complete purchases — orchestrating A2A, AP2 and MCP across the commerce journey.
- **Spec:** https://ucp.dev
- **Source:** Open commerce-interoperability standard, Apache-2.0, release v2026-04-08: https://ucp.dev and https://github.com/universal-commerce-protocol/ucp . Secondary attribution (Google/Shopify/Walmart, NRF 2026) and AAIF hosting per research §2 + trade press — flagged for primary verification at build (possible distinct 'UCP' efforts).

```
UCP: an open standard enabling interoperability between commerce entities for agent-driven shopping.
```

### MPP — Machine Payments Protocol (mpp)

- **Layer:** payments
- **Creator:** Stripe + Tempo
- **Status:** live (shipped 2026; IETF Internet-Draft) (2026)
- **What:** Stripe and Tempo's open standard for billing AI agents over HTTP — agents discover prices, pay, subscribe and reconcile across stablecoins, cards and BNPL, with cryptographic receipts.
- **Spec:** https://stripe.com/blog/machine-payments-protocol
- **Source:** Stripe + Tempo Machine Payments Protocol (shipped 2026-03-18; formalizes HTTP 402; price discovery + subscriptions + reconciliation; stablecoin via Tempo, cards via Stripe/Visa, Bitcoin via Lightning; Stripe PaymentIntents settlement; IETF Internet-Draft; 100+ services directory): https://stripe.com/blog/machine-payments-protocol . Listed for addition in research §2.

```
HTTP 402 + machine-readable price discovery → pay (stablecoin/card) → cryptographic receipt, in one cycle.
```

### Kite — Kite (Agent payments / identity infrastructure) (kite)

- **Layer:** payments
- **Creator:** Kite AI
- **Status:** live (Kite Chain + Agent Passport, 2026) (2025)
- **What:** A payments-and-identity layer for the agent economy: verifiable agent identities (Agent Passport), cryptographically enforced spending constraints, and stablecoin rails, integrating x402, AP2 and MCP.
- **Spec:** https://gokite.ai
- **Source:** Kite agent payments-and-identity infrastructure (Kite AIR identity / Agent Passport, SPACE framework, stablecoin rails; x402 envelope + AP2 settlement + MCP), Kite Chain + Agent Passport launch reported 2026-04-30: https://gokite.ai/kite-whitepaper ; Coinbase Ventures/x402 collaboration https://www.globenewswire.com/news-release/2025/10/27/3174837/0/en/kite-announces-investment-from-coinbase-ventures-to-advance-agentic-payments-with-the-x402-protocol.html . Listed for addition in research §2.

```
Kite AIR: verifiable agent identity + programmable spend constraints + stablecoin rails (x402 / AP2 / MCP).
```

### Visa TAP — Visa Trusted Agent Protocol (visa-tap)

- **Layer:** payments
- **Creator:** Visa (with Cloudflare)
- **Status:** live (launched Oct 2025) (2025)
- **What:** An open specification that signs an AI agent's identity into HTTP request headers so any merchant can cryptographically verify the agent is legitimate before agent-driven checkout.
- **Spec:** https://developer.visa.com/capabilities/trusted-agent-protocol
- **Source:** Visa Trusted Agent Protocol: open spec signing agent identity into HTTP headers via RFC 9421 / Web Bot Auth, Ed25519, Visa key directory, launched with Cloudflare ~2025-10-14, 12 launch partners, layers over ACP/UCP: https://github.com/visa/trusted-agent-protocol , https://developer.visa.com/capabilities/trusted-agent-protocol , https://investor.visa.com/news/news-details/2025/Visa-Introduces-Trusted-Agent-Protocol-An-Ecosystem-Led-Framework-for-AI-Commerce/default.aspx . Listed for addition in research §2.

```
RFC 9421 HTTP message signatures over Web Bot Auth → merchant verifies agent against Visa's key directory.
```

## Licensing & Access Economics — terms, compensation and gating

### RSL — Really Simple Licensing (rsl)

- **Layer:** licensing
- **Creator:** RSL Collective (Reddit, Yahoo, Medium, O'Reilly and others)
- **Status:** emerging standard (2025)
- **What:** Machine-readable content-licensing terms, referenced from robots.txt — say which AI uses are free and which require a license or royalty.
- **Spec:** https://rslstandard.org
- **Source:** First published 2025-09-10; RSL 1.0 official spec 2025-12-10: https://rslstandard.org/press/rsl-1-specification-2025 and https://rslstandard.org/press/rsl-standard . Enforced_by Cloudflare: research §2.

```
robots.txt:  License: https://example.com/license.xml   →   <rsl> ... <permits>search</permits> ... </rsl>
```

### Pay Per Crawl — Cloudflare Pay Per Crawl (pay-per-crawl)

- **Layer:** licensing
- **Creator:** Cloudflare
- **Status:** live (beta, 2025) (2025)
- **What:** Cloudflare's HTTP 402-based mechanism that lets publishers charge AI crawlers per request — allow free, set a price, or block — with Cloudflare as merchant of record.
- **Spec:** https://blog.cloudflare.com/introducing-pay-per-crawl/
- **Source:** Launch (private beta, July 1 2025), HTTP 402 + crawler-price/crawler-exact-price headers, Cloudflare as merchant of record: https://blog.cloudflare.com/introducing-pay-per-crawl/ . Seed triple (Web Bot Auth verifies pay-per-crawl): research §2.

```
HTTP/1.1 402 Payment Required
crawler-price: USD 0.01   →   crawler retries with: crawler-exact-price: USD 0.01
```

### Content Signals — Cloudflare Content Signals Policy (content-signal)

- **Layer:** licensing
- **Creator:** Cloudflare
- **Status:** live (2025) (2025)
- **What:** A robots.txt extension that lets a site declare how its content may be used after access — search, ai-input, and ai-train — as machine-readable preferences.
- **Spec:** https://blog.cloudflare.com/content-signals-policy/
- **Source:** Launch 2025-09-24, three signals (search / ai-input / ai-train), robots.txt extension, CC0, Cloudflare managed-robots default search=yes/ai-train=no, contentsignals.org: https://blog.cloudflare.com/content-signals-policy/ . Listed for addition in research §2.

```
# robots.txt
Content-Signal: search=yes, ai-input=yes, ai-train=no
```

## Governance — the bodies that steward the standards

### AAIF — Agentic AI Foundation (aaif)

- **Layer:** governance
- **Creator:** Linux Foundation (anchored by contributions from Anthropic, Block, OpenAI and others)
- **Status:** active (formed Dec 2025) (2025)
- **What:** The Linux Foundation body, formed December 2025, that gives the agentic web's load-bearing protocols — MCP, goose and AGENTS.md — a neutral, vendor-independent governance home.
- **Spec:** https://aaif.io
- **Source:** Formation date (Dec 9 2025), Linux Foundation parent, 8 platinum members (AWS, Anthropic, Block, Bloomberg, Cloudflare, Google, Microsoft, OpenAI), founding contributions MCP/goose/AGENTS.md: https://www.linuxfoundation.org/press/linux-foundation-announces-the-formation-of-the-agentic-ai-foundation . A2A v1.0/UCP hosting per research §2 (verify at build).

```
AAIF (Linux Foundation) hosts MCP, goose and AGENTS.md under neutral, open governance.
```

### W3C — World Wide Web Consortium (w3c)

- **Layer:** governance
- **Creator:** Tim Berners-Lee (founded 1994)
- **Status:** active (1994)
- **What:** The international web standards body that incubates agentic-web specs such as WebMCP (via its Web Machine Learning Community Group) and stewards the schema.org and Verifiable Credentials foundations agents build on.
- **Spec:** https://www.w3.org
- **Source:** W3C as the standards body developing WebMCP via the Web Machine Learning Community Group: https://webmachinelearning.github.io/webmcp/ . W3C founding/role: https://en.wikipedia.org/wiki/World_Wide_Web_Consortium . Seed triple (WebMCP standardized_by W3C): research §2.

```
W3C standardizes web specs; the Web Machine Learning CG develops the WebMCP draft.
```