MCP Glossary - Model Context Protocol Terms¶

A comprehensive reference dictionary of terms, definitions, and concepts used throughout the Model Context Protocol ecosystem. Essential for developers, architects, and AI engineers working with MCP implementations.

A¶

Agent¶

An AI system that can autonomously perform tasks using MCP tools and resources. Agents act as MCP clients.

Arguments¶

Parameters passed to MCP tools or prompts. Always validated against a JSON Schema.

Authentication¶

The process of verifying the identity of an MCP client or server. Supports multiple methods including OAuth 2.0, API keys, and mTLS.

Authorization¶

Determining what actions an authenticated client can perform. MCP implements fine-grained permission models.

B¶

Batch Request¶

Multiple JSON-RPC requests sent in a single message for improved efficiency.

Binary Transport¶

A transport mechanism that sends data in binary format rather than text, useful for performance-critical applications.

C¶

Capability¶

A feature that a client or server supports. Capabilities are negotiated during connection initialization.

Client¶

An application (typically an AI model or assistant) that connects to MCP servers to use tools and access resources.

Connection¶

An active communication channel between an MCP client and server over a transport.

Content¶

The data returned by tools, resources, or prompts. Can be text, images, or other MIME types.

Context¶

Information about the current state and environment available to the AI model when making MCP requests.

D¶

Discovery¶

The process by which clients learn about available tools, resources, and prompts from a server.

E¶

Error Code¶

Standardized numeric codes used to indicate specific error conditions in MCP responses.

Execution¶

The act of running a tool with provided arguments and returning results.

F¶

Function Schema¶

JSON Schema definition describing a tool's parameters, used for validation and documentation.

G¶

Gateway¶

An MCP server that provides access to multiple backend services through a unified interface.

H¶

Handler¶

A function in an MCP server that processes specific types of requests (tools, resources, prompts).

HTTP Transport¶

Communication mechanism using HTTP/HTTPS for client-server interaction.

I¶

Initialization¶

The handshake process where client and server exchange capability information.

Input Schema¶

JSON Schema that defines the expected structure of tool or prompt arguments.

Integration¶

Connecting an external service or tool to make it accessible via MCP.

J¶

JSON-RPC¶

The message protocol used by MCP. Version 2.0 specifically.

JSON Schema¶

The standard used to describe and validate the structure of data in MCP.

L¶

Lifecycle¶

The stages of an MCP connection: connecting, initializing, active, closing.

List Changed Notification¶

A server notification that available tools, resources, or prompts have changed.

M¶

Message¶

A single JSON-RPC request or response exchanged between client and server.

Method¶

The operation being requested in a JSON-RPC message (e.g., "tools/call", "resources/read").

MIME Type¶

Media type indicator for resource content (e.g., "text/plain", "application/json").

MCP¶

Model Context Protocol - the standard for AI-to-tool communication.

N¶

Notification¶

A message sent without expecting a response, used for events like capability changes.

O¶

OAuth¶

Authentication protocol supported by MCP for secure client authorization.

P¶

Parameter¶

An individual argument passed to a tool or prompt.

Permission¶

A specific action that a client is allowed to perform on a server.

Prompt¶

A reusable template for common interactions, with variable substitution support.

Protocol Version¶

The version of MCP being used, ensuring compatibility between clients and servers.

R¶

Request¶

A message from client to server asking for an operation to be performed.

Resource¶

A data source exposed by an MCP server, identified by a URI.

Response¶

A message from server to client containing the result of a request.

Result¶

The success output of an MCP operation, contained in the response.

S¶

Schema¶

JSON Schema definition for validating data structures in MCP.

Server¶

An application that exposes tools, resources, and prompts to MCP clients.

Session¶

An active connection between a client and server with maintained state.

Standard I/O (stdio)¶

Transport using standard input/output streams, common for local processes.

Streaming¶

Sending data progressively rather than all at once, supported for large responses.

Subscription¶

Client registration to receive updates when resources change.

T¶

Tool¶

A function exposed by an MCP server that clients can execute with parameters.

Transport¶

The communication layer that carries MCP messages (stdio, HTTP, WebSocket).

Type¶

The data type of a parameter or return value, defined in JSON Schema.

U¶

URI¶

Uniform Resource Identifier used to uniquely identify MCP resources.

Unique ID¶

Identifier for matching requests with responses in JSON-RPC.

V¶

Validation¶

Automatic checking of tool arguments against their schema before execution.

Version¶

The protocol version, ensuring compatibility between implementations.

W¶

WebSocket¶

Bidirectional transport protocol enabling real-time MCP communication.