MCP Tool
An MCP tool is a named, typed function exposed by an MCP server that an AI agent can call with structured arguments to read data or take an action.
In plain English
An MCP tool is a function — with a name, a description, an input schema, and an output schema — that an AI agent can call over the Model Context Protocol. The AI decides when to invoke it and what arguments to pass; the server executes it and returns the result. Tools are how agents reach beyond text into the world.
Good tool design matters as much as good prompt design. A tool with a crisp description and a tight input schema will be used correctly. A tool with a vague description and a kitchen-sink input will be misused or ignored. Names, descriptions, and arguments are part of the agent's "API," and they should be designed for language-model ergonomics as deliberately as any public SDK.
Why it matters for Black Box
Every specialist in Black Box has a tool belt — a curated list of MCP tools appropriate to its role. The Content specialist does not get shell access. The Coding specialist does not get Stripe payout tools. Constraining the tool set is how the product keeps quality high and risk low.
Examples
files.write— takes a path and content, writes to disk.calendar.create_event— takes a title, time, attendees, returns an event ID.stripe.create_invoice— takes a customer and line items, returns an invoice URL.