MCP Advertising Audit

There's a discovery pattern the modern web hasn't had to think about before: an AI agent visiting your site, looking not for a page to render but for an action to call.

Updated October 13, 2026: I corrected what the MCP file and the agent card actually describe. An MCP server card lists no tools, and an agent card is for an A2A agent. I also added the AI catalog (/.well-known/ard.json), the file that ties them together.

The agent's question isn't "what does this site say?" That's the RAG question, solved by content. The agent's question is "what can this site do for me on behalf of my user?"

Answering that requires a new kind of advertising. Not marketing. Machine-readable advertising. A tiny set of well-known JSON files that say: here's who I am, here's what I can do, here's how to call each action, here's what auth I need.

Most sites have zero of these files. Every one will need at least one by the end of 2026.

The well-known discovery surface

There are (as of early 2026) five manifest paths that matter, plus a handful of secondary ones:

High priority:

/.well-known/ai-plugin.json: the ChatGPT-plugin format. Oldest, most widely supported. Describes auth, API location, logo, legal info.
An MCP server card. This is the Model Context Protocol's own discovery file (SEP-2127, status Final). It describes the server's identity (name, version, description), its remote endpoints and the protocol versions they speak. It deliberately lists no tools, resources or prompts. A client connects to the endpoint and calls tools/list to get those at runtime. The recommended address is your MCP endpoint plus /server-card (for example https://yourdomain.com/mcp/server-card). Some scanners still read /.well-known/mcp.json and /.well-known/mcp/server-card.json, so I serve the same bytes there too.
/.well-known/agent-card.json: the A2A agent card. It describes an A2A agent, something that accepts A2A messages at an endpoint, along with its skills and interfaces. It is not a general site identity file. Don't publish one unless you run an A2A endpoint that answers it.
/.well-known/ard.json: the AI catalog (Agentic Resource Discovery). This is the site-wide index that ties the others together. Each entry points to a card: the MCP server card with type application/mcp-server-card+json, the A2A agent card with type application/a2a-agent-card+json. The chain is catalog, then card, then endpoint. The older address /.well-known/ai-catalog.json is legacy, so I publish one file at both.

Medium priority:

/.well-known/openapi.json or /openapi.yaml: OpenAPI spec defining your HTTP API surface. Needed if ai-plugin.json references it.
/.well-known/ai.txt: your general AI policy (separate from this, covered by other tools in the jwatte set).
/llms.txt: LLM-readable sitemap; also covered separately.

Low priority / emerging:

/asyncapi.json: event-driven API contracts (rare in the SMB context).
/.well-known/agents.txt: very early proposal for agent-specific robots-style rules.

What the MCP Advertising Audit does

You paste your domain. The tool:

Probes each of those paths. Reports 200 OK + whether the response is valid JSON.
Scores your MCP-readiness (weighted by importance) from 0-100.
Crawls your homepage's JSON-LD and counts Schema.org PotentialAction nodes, because a site that already advertises ReserveAction or SearchAction in schema is ahead of the curve.
Generates starter snippets for any missing high-priority manifest. You copy, customize with real tools/auth, deploy at the path.
Emits an AI fix prompt that reasons about which of these you actually need for your specific business type.

Who actually needs each manifest

E-commerce sites need ai-plugin.json + OpenAPI more than MCP. Agents need to search products, add to cart, check availability. The ChatGPT plugin format has been optimized for this workflow for two years.

Service businesses (legal, medical, trades) need MCP, plus agent-card.json only if they run an A2A agent. Agents need to book consultations, request quotes, check availability. MCP's tool schema is better for structured, multi-step conversational flows.

Publishers / content sites need llms.txt first. An agent card only makes sense if you run an A2A agent. Agents aren't buying from you; they're citing you. Your manifests should optimize for accurate citation and freshness signaling.

SaaS companies need all three, ideally. They're being called by copilot clients that could replace chunks of human SaaS work. First-mover advantage is real here.

The "what tools should I expose" problem

Every SMB owner asks the same three things:

Which of my actions should be callable by an agent?
How do I prevent agents from abusing the endpoint?
What do I get out of it?

For #1: start with public, read-only actions. A quote calculator. A product search. An availability check. A service-area verification. These have zero risk and maximum upside.

Actions requiring auth (booking, ordering, payment) come next. Require API keys or OAuth. Rate-limit aggressively. The MCP spec supports auth; ai-plugin.json supports it; agent-card.json supports it.

For #2: three layers of defense.

Origin allowlist (the same pattern the jwatte.com functions use)
Per-IP rate limits per tool
Manifest-declared rate_limit field so honest agents back off before hitting your server-side limits

For #3: the short-term payoff is being cited in agent answers. The medium-term payoff is being the preferred vendor an agent picks when its user says "find me a roofer in Twin Falls." The long-term payoff is survival in a world where AI-mediated commerce is the dominant retail interface.

The 30-day rollout plan

Week 1: Probe current state with this tool. Pick the 2-3 manifests matching your business type. Week 2: Write an OpenAPI spec for your 2-3 most callable actions (usually: search, quote, contact). Week 3: Deploy the manifests and a backing MCP server (or HTTP API) that implements the declared tools. Week 4: Test with Claude Desktop + ChatGPT + one agent framework. Fix the things that break.

At day 30 you're ahead of ~98% of your competitive set. The window for that asymmetry closes by end of 2026 as manifest authoring gets baked into every SaaS offering.

Why SMBs should care now, not later

Fortune 500 companies are adopting MCP on the order of weeks. By the time they notice the standard exists, they can deploy in a sprint. An SMB that adopts first gets to be the answer when an agent asks "find me a local [category] that my user can book directly." There's no rematch on first-mover position; once the pattern of "this vendor's agents book directly" sets in, incumbents keep winning.

The technical cost is a day of work. The upside is structural. That ratio is nearly unique in SMB tooling history.

Fact-check notes and sources

Model Context Protocol spec: modelcontextprotocol.io
OpenAI ai-plugin.json spec: documented at platform.openai.com (legacy but widely implemented)
Well-known URI registry (IETF): iana.org/assignments/well-known-uris
Schema.org PotentialAction: schema.org/potentialAction
October 13, 2026 update: the MCP server card shape (identity, remotes endpoints, protocol versions, no tools/resources/prompts; recommended address is the MCP endpoint plus /server-card) is from SEP-2127 MCP Server Cards (status Final) and the wire format in ext-server-card (schema.json, docs/discovery.md), read October 13, 2026. The A2A agent card at /.well-known/agent-card.json describing an A2A agent is from the A2A protocol specification, read October 13, 2026. The AI catalog at /.well-known/ard.json and its entry types are from Agentic Resource Discovery v0.91 (status Proposal), read October 13, 2026.

This post is informational, not engineering or agent-integration consulting advice. Mentions of Anthropic, OpenAI, Google, LangChain, LlamaIndex, CrewAI, Cursor, and the Model Context Protocol are nominative fair use. No affiliation is implied.

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