MCP (Model Context Protocol)

 gave an AI agent write access to a production system.

Not a demo. A real internal tool people depend on. It can now read, create, and update records - in plain language, from a chat window.

Four things I learned building it with MCP (Model Context Protocol):
1. The tool description IS the interface. The agent doesn't read your code. It reads one sentence describing each tool, and decides from that alone whether to call it. Write "internal API test" → ignored forever. Write "creates and updates support tickets" → fires correctly. We spent 15 years designing UIs for humans. The design surface is now a sentence a model reads.

2. Agents can't click "Sign in." Any auth flow expecting a browser redirect silently breaks an agent connection. Machine access and human access need separate doors into the same house.

3. MCP errors don't mean what you think. My server returned success on every request -and the agent still failed. A "404" in MCP means session expired, not wrong URL. New protocol, new error vocabulary.

4. Least privilege stops being optional the moment an agent can write. A human with too many permissions makes occasional mistakes. An agent makes them at machine speed, confidently, while explaining why it was right.

Why this matters:
MCP turns "integrate AI into our systems" from a bespoke project into a standard interface. Expose capabilities, describe them clearly, and any compliant agent can use them.
Same shift APIs caused 20 years ago - except the consumer isn't a program following rigid contracts. It's a model deciding at runtime what to call and why.
The interfaces we built for humans aren't going away. They're just no longer the only way in.

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