MCP Glossary

The MCP Glossary defines 20 core terms and concepts. Each definition is evidence-backed and includes the protocol-level mechanics you need to understand MCP servers, clients, and the JSON-RPC layer.

• Model Context Protocol (MCP)

  Definition of the Model Context Protocol — an open protocol for connecting AI applications to external tools and data sources.

• JSON-RPC 2.0 in MCP

  JSON-RPC 2.0 is the message format used by MCP for requests, responses, and notifications.

• MCP Tool

  An MCP tool is a callable function exposed by a server with a name, description, and input schema.

• MCP Resource

  An MCP resource is addressable data exposed by a server, identified by a URI and returned with a MIME type.

• MCP Prompt

  An MCP prompt is a reusable invocation template a server exposes, with arguments that fill the template.

• MCP Transport

  MCP supports two transports: stdio for local servers and Streamable HTTP for remote servers.

• MCP Initialize Handshake

  The initialize handshake negotiates protocol version and capabilities before any primitive operations.

• MCP Capability Negotiation

  During initialize, client and server declare supported capabilities to establish a common baseline.

• Server-Sent Events in MCP

  SSE is used by the Streamable HTTP transport for server-to-client streaming and notifications.

• Bearer Token Authentication

  A bearer token proves identity by possession. The client includes it in the Authorization header for remote MCP servers.

• OAuth 2.0 for MCP

  MCP supports OAuth 2.0 for delegated authorization of remote servers with scopes.

• OAuth Scope

  An OAuth scope bounds what an authenticated caller may do — down to individual tools or resources.

• Read-Only Mode

  Read-only mode restricts a server's exposed tools to operations that do not mutate state.

• Prompt Injection

  Prompt injection is untrusted content that tries to steer an AI agent against the user's intent.

• Tool Poisoning

  Tool poisoning is when a malicious server exposes misleading tool descriptions to trick an agent into harmful operations.

• Least Privilege Principle

  Least privilege grants the minimum access a task requires — applied to tools, credentials, and scopes.

• server.json Metadata

  server.json is a metadata format describing an MCP server for registry publication and discovery.

• MCP Registry

  An MCP registry stores machine-readable server metadata for programmatic consumption by clients and verification tools.

• MCP Directory

  An MCP directory is a human-searchable catalog of servers for browsing and comparison.

• MCP Marketplace

  An MCP marketplace adds install/purchase flows on top of a directory.