MCP, WebMCP, A2A, ACP, UCP and NLWeb explained
Six protocols are competing to define how AI agents connect to tools, to each other, to shops and to websites. Two are settled enough to build on (MCP, A2A). Two are backed by large companies but less than a year old (ACP, UCP). Two are proposals a website owner should watch but not re-platform for (WebMCP, NLWeb). Here is what each one is, from the public record.
Agents connecting to tools
MCP (Model Context Protocol). An open standard that lets an AI application connect to external tools and data through servers that describe what they offer, so a model can call a tool the same way whichever vendor built it. Anthropic released it in November 2024, OpenAI, Google and Microsoft adopted it during 2025, and in December 2025 Anthropic moved its governance to a Linux Foundation project. It is the most widely implemented of the six. For a website owner it means a way to expose search, product lookup or account actions to agents as named tools rather than as pages to scrape.
WebMCP. A proposal from Google and Microsoft engineers, developed in a W3C community group, that lets a web page declare tools an agent running in the browser can call directly, through a JavaScript API or declarative markup, instead of clicking through the human interface. Chrome shipped an early developer preview in 2026. It is early: the API is changing, no other browser has committed, and there is no agreement yet on how a page's declared tools interact with robots.txt or with agents that do not run a browser. Worth reading, not yet worth building a roadmap around.
Agents talking to agents
A2A (Agent2Agent). Google's protocol, announced in April 2025 and donated to the Linux Foundation in June 2025, for one agent to discover another, exchange tasks and return results. Each agent publishes a JSON "agent card" at a well-known URL describing what it can do. Where MCP connects an agent to tools, A2A connects an agent to other agents. For a website owner it is mostly relevant if you intend to run an agent of your own that other companies' agents can call.
Agents buying things
ACP (Agentic Commerce Protocol). The acronym collides: IBM used it for an agent communication protocol and the editor Zed for an agent client protocol. In commerce it means the specification OpenAI and Stripe published in September 2025 that lets a merchant accept an order placed inside ChatGPT, with a shared payment token so the merchant stays the merchant of record. It powers ChatGPT's Instant Checkout. It is one company's checkout surface, published as an open spec, and it is under a year old.
UCP (Universal Commerce Protocol). Google's answer, announced in January 2026 with large retailers and commerce platforms as launch partners, for buying inside Google's AI surfaces and for agents to transact with merchants. Google positions it as interoperating with A2A, MCP and its payments protocol. Also under a year old. The practical reading: two of the largest agent operators have each published a checkout protocol, they are not the same protocol, and merchants may need to speak both.
Websites answering questions
NLWeb. Microsoft's open-source project, released at Build in May 2025, for giving a website a natural-language interface over its own content. It builds on the Schema.org markup most sites already publish, and every NLWeb endpoint also acts as an MCP server, so an agent can query a site in plain language rather than scraping its pages. Adoption is modest so far and the project is still shaped mostly by Microsoft. Of the six, it is the one aimed most directly at publishers and brands rather than at platforms.
What a website owner should do
Not re-platform. Each of these needs a server-side endpoint on your domain, and four of the six have changed materially inside twelve months. The sensible place to put them is the agent-facing side of your site: a bot CDN already routes identified agents to a surface you control, serves them the sitemap and robots.txt they read, and runs on top of your existing CDN or WAF. An MCP endpoint, an NLWeb endpoint or a WebMCP tool declaration can be added or retired there each quarter without touching the human site.
Frequently asked questions
Do I need MCP to be visible to AI agents? No. Agents read ordinary HTML pages today, 200M+ fetches a day across our network. MCP adds a cleaner way to expose actions. Readable pages come first.
Which of these will win? MCP for tools is the only one with multi-vendor adoption and open governance today. A2A is close behind for agent-to-agent. The commerce protocols are a two-horse race with no result yet, and WebMCP depends on browsers other than Chrome.
Is NLWeb a replacement for my site search? No. It is an additional interface for agents, built from your structured data. Human search stays where it is.