Once you're giving a model tools and data, a practical problem shows up fast: every tool, every data source, every model wired to every one of them is a bespoke integration. Connect three models to four data sources and you're maintaining a dozen custom connectors. The Model Context Protocol (MCP) is the standard that turns that mess into a common interface. It's increasingly how models and tools get wired together, so it's worth knowing what it actually is.
Why this matters for the job
The value is the classic integration math. Without a standard, connecting N models or apps to M tools is an N × M problem. Every pairing is custom. With a shared protocol, each tool implements the standard once and every compatible client can use it: N × M collapses to N + M. For an FDE dropping into a customer with a dozen internal systems, that's the difference between a dozen one-off connectors and a set of reusable servers. It matters most where you integrate many tools or serve many customers.
It's also a concrete hiring signal at Anthropic, whose FDE role names shipping "MCP servers, sub-agents, and agent skills" to production (see Company Differences). If you're targeting an MCP-native shop, being able to explain and build against the protocol is close to expected.
Before reading on: you're integrating an assistant with a customer's ticketing system, their CRM, and their internal wiki. Without a standard, what does adding a fourth system next quarter cost you, and what would a protocol change?
Without a standard, each system is a custom connector you build and maintain, and the fourth is a fourth bespoke integration. The cost grows with every tool and every model. A protocol makes each system a server that implements the interface once; the fourth just implements the same standard, and every current and future client can use it without new glue.
What MCP actually standardizes
- A client-server model. The application (the host, via a client) talks to servers that wrap tools and data. The customer's ticketing system becomes an MCP server; your assistant is a client that can use any such server.
- Three things a server exposes: tools (functions the model can call), resources (data the model can read), and prompts (reusable templates). The tool-use round trip you already know is what's happening underneath, now over a shared interface.
- A standard message format. Communication uses a common protocol (JSON-RPC-based), so a client and server written by different people, at different companies, interoperate without custom code.
- A versioned spec. MCP is date-versioned and evolving (currently revision 2025-11-25). Pin the version you build against, because the standard is still moving.
The same safety thinking from tool use applies unchanged: a tool exposed over MCP is still an action to validate and bound, and a server that reads untrusted content is still an injection surface. Reuse cuts the other way too: a server you carry from one customer to the next still needs that customer's own credentials and a fresh security review, because the interface is portable but the trust setup is not. A standard interface makes integration easier; it does not remove the trust boundary.
Bad / Good / Great — "how do you connect the model to the customer's tools?"
Bad — "I'd write custom API integrations for each tool." Workable for one or two, unmaintainable at a dozen, and it ignores that a standard now exists. It signals you're a version behind the field.
Good — "I'd use MCP so tools connect through a standard interface." Correct and current. You know the standard and why it helps. The gap: no sense of when the standard earns its cost, or that the security boundary is unchanged.
Great — "Where I'm integrating many tools or serving many customers, MCP: each system becomes a server exposing tools and data through the standard, so I turn an N×M integration problem into N+M and reuse servers across engagements. For one or two simple tools, a direct integration is fine; the standard earns its keep at scale. Either way the tool boundary still needs validation and bounding." You named the protocol, the integration math, and when it's worth it, with the safety caveat intact.
What to carry into the interview
Knowing MCP exists and what it standardizes is assumed at MCP-native labs; what gets graded is the judgment: it's an integration-scaling standard, worth it when you're wiring many tools or many customers, and it doesn't change the fact that every tool is still an action to guard.
Next: Evaluations. You've now walked every block, from the prompt to the standard that wires them together; next comes the discipline that makes the system survive a real customer.NextEvaluations