Founders keep hearing “we added MCP” the way they used to hear “we added an API.” Both sentences are empty until someone names the permission.
What MCP actually is
MCP is a way for a model to call tools through a shared contract. The model asks. A server exposes tools. The host decides what is allowed. That is the whole shape.
You do not need the spec memorised. You need three answers in writing for every server you attach to an agent:
- Visibility. What can this tool read? Files, mail, a database, a customer list.
- Mutation. What can it change, send, or delete?
- Log. Where does the call land so a human can reconstruct Tuesday?
If any answer is “it depends,” the server is not ready. “It depends” is how a helpful agent mails a customer from a draft you never approved.
What MCP is not
It is not a moat. Competitors can attach the same protocol.
It is not safety by itself. A protocol that can write is as dangerous as any other write API.
It is not a substitute for STACK. STACK is the five-layer repo architecture: structure, toolchain, agent configuration, connection, knowledge and quality. MCP sits in the connection layer. If your rules live in five tools and your MCP servers have no owners, you have agentic repo debt. The protocol did not cause it. The missing contract did.
A founder review in fifteen minutes
Ask the person who “added MCP” to walk a single tool.
- Who owns this server in the repo?
- What is the authority ceiling?
- What does the override doctrine forbid this tool to do?
- If it sends, spends, or deletes, who reviews the first ten calls?
- If we unplug it at 17:00, what breaks?
You are not asking for a demo. You are asking for the same things you ask of a new production integration. Treat it that way and MCP becomes boring, which is the goal.
The public specification is the first-party source for field names. Re-read it before you pin a version. This page will not keep up with every wrapper.
Where this sits
The Agentic Codebase is the book that treats the agent OS as something you version like the app. What is an AI agent? is the definition of the worker. MCP is how that worker is allowed to touch the building.