Terminology

This glossary defines key terms you'll encounter when working with MCP clients and servers. It includes foundational concepts, communication structures, and configuration terms commonly used during setup, testing, and deployment.

Core Concepts

MCP (Model Context Protocol)
A lightweight protocol that allows AI clients to invoke structured tools provided by external servers.

MCP Server
A standalone program (Node.js or Python) that exposes callable tools using the MCP schema and responds over a supported connection type.

MCP Client
An interface (e.g., AI chat, command line, dashboard) that connects to an MCP server, discovers its tools, and triggers tool executions.

Tool
A unit of functionality defined by an MCP server. Each tool includes a name, description, input schema, and an execute() method.

Tool Call
A request from the client to invoke a specific tool with parameters, following MCP JSON format.

Capabilities File (capabilities.json)
A JSON manifest listing all tools a server provides, their schemas, and metadata. This is how clients discover what a server can do.

Prompt Template
A predefined instruction that guides the AI’s response style or behavior during tool usage. Configured on the client side.

Resource
A data object (e.g., file, folder, image) referenced in context but not directly executed like a tool. Resources often support agent reasoning.

Connection Types

STDIO (Standard I/O)
A local connection method where the server is launched as a subprocess and communicates via standard input/output streams.

SSE (Server-Sent Events)
A remote connection method where the client receives streamed JSON responses from a web-based API server.

Configuration Parameters

Command
The system command used to launch the server (required in STDIO mode), "python" or "node".

Arguments (Args)
A list of arguments passed to the command (usually the server script path), ["index.js"].

Environment Variables (Env)
Optional variables used to configure runtime behavior (e.g., auth paths, system tools), { "UV_PATH": "/usr/bin/uv" }.

Server URL
The entry point for an SSE-based server (usually a web API endpoint), "https://api.example.com/mcp".

Headers
Optional metadata or authentication passed in HTTP requests for SSE servers, { "Authorization": "Bearer token" }.

Server Type
Declares the connection method (STDIO or SSE) when adding or registering a server, "stdio" or "sse".

Debugging & Testing

MCP Playground / Inspector
A visual testbed for connecting to MCP servers, running tools, and viewing results in real time. Useful for debugging before deploying.

Tool History
A log of previous tool calls and their outcomes (input → output). Helpful for reviewing session behavior.

Session
A persistent communication state between a client and a server, allowing tools to be called with context.