MCP, A2A, and WebMCP are the three protocols that determine whether a website is something an AI agent can query and transact with, or only look at. Two are production-ready open standards under Linux Foundation governance, adopted across AWS, Google, Microsoft, Salesforce, and SAP. The third is a Chrome-only browser draft, still widely misdescribed as settled.
How the Combinatorial Problem Got a Common Interface
Before these standards existed, every connection between a model and an external system was a bespoke integration. The number of integrations grew as the product of models and tools rather than their sum, a combinatorial problem that scales faster than any team can maintain.
MCP borrows its architectural logic from the Language Server Protocol, which solved the same shape of problem for code editors: many editors, many languages, and an integration matrix that expanded until someone defined a common interface between them. The framing carries over directly. Define a standard once, and every model and every tool that adopts it gets interoperability with all the others for free.
The same constraint applies to websites. A site that renders only for human eyes forces any visiting agent into actuation, simulating clicks and keystrokes against an interface never designed to be read by a machine. Each inferred step is a point of silent failure, and silent failures at machine speed are expensive.
💡 Practical note: Actuation fails silently; if your checkout depends on an agent correctly operating a custom date picker, assume a meaningful share of agent-initiated transactions never complete.
MCP: The Tool Access Layer
MCP defines how an AI application connects to external systems. An agent discovers a server, the server exposes tools with typed inputs and outputs, and calls travel over JSON-RPC. The protocol operates on three primitives: resources for read-only data, tools for actions, and prompts for standardized templates.
Anthropic released MCP in November 2024 and donated it to the Agentic AI Foundation, a directed fund under the Linux Foundation co-founded with Block and OpenAI, on December 9, 2025. Platinum members include AWS, Anthropic, Block, Bloomberg, Cloudflare, Google, Microsoft, and OpenAI. Direct competitors placed a shared connective layer under neutral stewardship, which is the condition that lets an operator build against it without betting on one vendor's roadmap.
Adoption figures reported at the donation announcement:
- Monthly SDK downloads
- 97 million+
- Active public servers
- 10,000+
- Governance
- Agentic AI Foundation (Linux Foundation)
- Client support
- ChatGPT, Claude, Cursor, Gemini, Copilot
- First released
- November 2024
The July 2026 Revision: MCP Goes Stateless
The largest revision since launch published on July 28, 2026. Its headline change is that MCP becomes stateless at the protocol layer.
The initialize handshake and the Mcp-Session-Id header are both removed. Any request can now land on any server instance, so a remote server that previously required sticky sessions and a shared session store runs behind an ordinary round-robin load balancer. Horizontal scaling stops being a protocol problem.
Servers that still need continuity across calls handle it the way HTTP APIs always have: mint an explicit handle from a tool and have the model pass it back as an argument. State becomes visible to the model rather than hidden in transport metadata.
The revision also hardens authorization against a mix-up attack class specific to MCP's single-client, many-server pattern, promotes extensions to first-class status, and deprecates roots, sampling, and logging under a lifecycle policy guaranteeing at least twelve months before removal.
This release gives MCP the foundation we expect it to grow on for a long time.
For a site operator, exposing an MCP server is now the standardized way to make a catalog, a booking system, or a pricing engine callable by an external agent without publishing a bespoke API for every counterparty.
A2A: The Agent Coordination Layer
Where MCP connects an agent downward to tools, A2A connects agents sideways to each other. Google announced it in April 2025 with more than 50 launch partners and donated it to the Linux Foundation two months later.
At its one-year mark, the project reported more than 150 supporting organizations, including AWS, Cisco, Google, IBM, Microsoft, Salesforce, SAP, and ServiceNow. Microsoft embedded it in Azure AI Foundry and Copilot Studio; AWS added support through Bedrock AgentCore Runtime. The core repository has passed 22,000 GitHub stars, and the SDK ecosystem expanded from a single Python implementation to five production-ready languages.
Version 1.0, the release that met the enterprise production bar, introduced multi-protocol support, enterprise multi-tenancy, Signed Agent Cards for cryptographic identity verification, and a web-aligned architecture supporting familiar security and load-balancing patterns.
The distinction from MCP is one of scope rather than competition, and both projects describe themselves as complementary:
| Dimension | MCP | A2A |
|---|---|---|
| Governs | Agent to tools and data | Agent to agent |
| Boundary | Within an organization | Across organizations |
| Discovery | Server capabilities | Signed Agent Cards |
| Identity | OAuth 2.0 / OIDC | Cryptographic agent identity |
| Governance | Agentic AI Foundation | Linux Foundation |
| Scale signal | 10,000+ public servers | 150+ organizations |
One caveat worth holding: supporting a standard spans a wide range of commitment. The announcement named production verticals without publishing deployment counts or usage metrics, so practical adoption is narrower than supporter counts alone suggest.
How Payments Fit in
Coordination alone does not close a sale. The Agent Payments Protocol extends A2A into economic exchange, with more than 60 organizations across payments and financial services backing it. Its core contribution is a cryptographic artifact capturing evidence of a user's consent to purchase.
That consent artifact answers an authorization question that ordinary web checkout never had to handle. A human clicking a button was itself the proof of intent. An agent spending money on someone's behalf creates a new chain of custody, and the protocol makes that chain auditable.
A distributor exposing specifications, compatibility, and live stock through MCP, reachable by a buyer's agent over A2A, with settlement handled under the payments protocol, can complete a machine-to-machine sale end to end. The catalog stops functioning as a storefront and starts functioning as a node that other systems transact against.
What WebMCP Is - and Is Not
WebMCP is routinely listed as the settled third pillar of the agentic stack. That framing runs well ahead of its status.
It is a proposal from the W3C Web Machine Learning Community Group, co-authored by Microsoft and Google engineers, available as an origin trial from Chrome 149. The concept is direct: a page registers callable tools through navigator.modelContext, so a browsing agent invokes checkout or filter_results rather than inferring intent from the DOM. Tools carry JSON Schemas for inputs and outputs, with both an imperative JavaScript API and a declarative path that annotates standard HTML forms.
Its constraints are equally direct. Tool calls execute in page JavaScript, so a browser context must be open and headless invocation is not possible. A client must visit a site directly to learn it has tools at all. No browser besides Chrome has shipped an implementation, and Firefox and Safari have not committed to timelines. Security is gated but unfinished, with open questions around prompt injection and destructive actions acknowledged rather than resolved.
The reasonable operator position is that WebMCP complements a server-side MCP integration rather than replacing one. Server-side exposure serves autonomous agents acting without supervision; the browser layer assists agents working alongside a person who is actively on the page. They answer different use cases.
What a Site Must Expose to Participate
Participation in this stack is not a plugin. It requires that the underlying business data exist in queryable form, which is the step most sites have not taken. A CMS optimized for rendering pages rarely exposes anything an external agent can call.
The minimum viable posture has three parts. Structured data an agent can read without parsing layout. An MCP server exposing the operations that matter commercially rather than a generic content endpoint. And live connection to the systems of record, so answers reflect current stock, pricing, and availability rather than a snapshot from last quarter.
That last requirement is where most implementations stall. A protocol layer over stale data produces confident wrong answers at machine speed, which is worse for a buyer's agent than no endpoint at all, because a wrong answer gets acted on. Sequencing matters: a structured MCP server with live inventory is worth more than an agent card pointing at a catalog nobody can query.
The architecture question a site owner faces is not which protocol to pick. It is whether the site's data and operations are exposed in a form that these protocols can reach at all.
