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· For normative definitions, follow the official MCP documentation.

Model Context Protocol — glossary

These entries explain how people use words when discussing MCP online: search engines, forums, and product docs. They are educational summaries, not a substitute for the specification text. Continue to protocol & architecture or the FAQ for narrative context.

Model Context Protocol (MCP)

The umbrella name for an open protocol that lets applications hosting LLMs connect to external systems through a shared client–server model. Public documentation describes MCP as a way to standardize how AI apps plug into data and tools—analogous to a common port shape for many devices.

MCP host

The host is the program users interact with that also manages model calls: an IDE, a desktop agent, a custom runtime, or similar. It is responsible for lifecycle, permissions, and which MCP servers are attached for a session. See roles on the architecture page.

MCP server

An MCP server is not necessarily a cloud VM—it is usually a long-lived process (often local) that speaks MCP on a supported transport and advertises tools, resources, and prompts. Business logic for a database, ticketing system, or internal API typically lives here.

Tool (MCP)

A tool is a callable capability with a schema: inputs the model can fill, outputs the host can return to the model, and (often) side effects in the outside world. Think “run this query” or “create this file,” not static documentation text.

Resource (MCP)

A resource is addressable content—files, URLs, records—that the user or model can read for grounding. Resources are closer to “documents you open” than to imperative actions.

Prompt (MCP)

A prompt in MCP is a packaged template or workflow offered by a server (distinct from the free-form chat the user types). It helps teams ship repeatable instructions alongside tools and resources.

Transport

The transport carries MCP messages between host and server. Local integrations frequently use stdio pipes; remote setups may use HTTP-based streaming transports defined in the current specification. Transport choice affects deployment, authentication, and threat modeling.

JSON-RPC (in MCP)

MCP frames many interactions as JSON-RPC 2.0 requests, responses, and notifications. You do not always author raw JSON-RPC by hand— SDKs abstract it—but understanding the pattern helps when debugging wire traces.

Capability negotiation

On connect, hosts and servers exchange capabilities: which primitives and protocol features each side supports. That negotiation keeps clients and servers interoperable across spec versions when features are optional.

MCP client (inside the host)

Documentation sometimes distinguishes the host application from an internal MCP client object that maintains sessions to servers. The user-visible “client app” is still the host; naming reflects code architecture inside SDKs.

See also