Glossary
41 terms used across this directory, from the act layer and MCP host to WebMCP and server cards. Each entry gives a one-line definition and an example with a source, so a reader and an agent can check the term against the specification it came from.
| Act layer | The part of agent readiness about completing tasks: MCP servers, CLIs, APIs with OpenAPI, WebMCP and agent payments. |
|---|---|
| Agent Card | The A2A JSON document describing an agent's skills, endpoints and auth, served at /.well-known/agent-card.json. |
| Agent Skills | A folder with a SKILL.md file of instructions and optional scripts that agents load on demand. |
| Agent2Agent (A2A) | A protocol for agents to discover each other and exchange tasks, now at version 1.0.0. |
| Agentic AI Foundation (AAIF) | The Linux Foundation-directed foundation that hosts MCP, A2A, goose and AGENTS.md. |
| agents.json | An OpenAPI-based file at /.well-known/agents.json describing flows of API calls for agents. |
| AI gateway | A proxy in front of model APIs that adds caching, rate limits, logs and billing across providers. |
| Client ID Metadata Document (CIMD) | A JSON file on the client's domain whose HTTPS URL is used as the OAuth client_id, the recommended MCP registration method. |
| Code Mode | A Cloudflare approach where the agent writes code against a typed API instead of calling many tools one by one, set by portal policy. |
| Confused deputy | An attack where a proxy with its own credentials is tricked into acting for someone else; MCP security guidance addresses it for OAuth proxies. |
| document.modelContext | The WebMCP entry point on the document object that holds registerTool, getTools and executeTool. |
| Dynamic Client Registration (DCR) | RFC 7591 registration where a client POSTs to /register for credentials; deprecated in MCP 2026-07-28 and kept for compatibility. |
| Elicitation | A way for a server to ask the user, through the client, for more information, now handled through multi round-trip requests. |
| HTTP+SSE transport | The older MCP HTTP transport with a separate SSE endpoint, deprecated since 2025-03-26 and reclassified Deprecated in 2026-07-28. |
| MCP Apps | An MCP extension in which a tool points to a ui:// resource the host renders as a sandboxed View. |
| MCP client | The connector inside a host application that holds one connection to one MCP server. |
| MCP gateway | A proxy in front of MCP servers that authenticates callers, injects upstream credentials, filters tools and logs calls. |
| MCP host | The LLM application that starts client connections and asks the user for consent. |
| MCP registry | A catalog of MCP server metadata that clients and directories read; the official one is registry.modelcontextprotocol.io. |
| MCP server | A program that exposes tools, resources or prompts to MCP clients over stdio or Streamable HTTP. |
| MCP server portal | Cloudflare's product that puts many MCP servers behind one authenticated endpoint with per-tool controls. |
| mcp-publisher | The CLI that publishes a server.json to the official registry after namespace verification. |
| Model Context Protocol (MCP) | A JSON-RPC 2.0 protocol in which hosts run clients that connect to servers offering tools, resources and prompts. |
| Multi round-trip request (MRTR) | The 2026-07-28 pattern where a server returns input_required and the client retries the request with the answers. |
| Namespace verification | Proof that a publisher controls a registry name, by GitHub login or OIDC for io.github names and DNS or HTTP for domains. |
| NLWeb | Microsoft's open project giving sites a natural-language ask method with Schema.org JSON responses; each instance is an MCP server. |
| Prompt | A templated message or workflow an MCP server offers to users. |
| Protected Resource Metadata | The RFC 9728 document an MCP server MUST publish to name its authorization servers and scopes. |
| Remote MCP server | An MCP server reached over the network, today through Streamable HTTP, rather than launched locally. |
| Resource | Context or data an MCP server offers for the user or model to read, addressed by URI. |
| Resource indicator | The RFC 8707 resource parameter that names the MCP server a token is for; clients MUST send it. |
| server.json | The registry metadata file for one server: name, version, remotes, packages, website and repository. |
| server/discover | The 2026-07-28 RPC every server MUST implement to advertise supported protocol versions, capabilities and identity. |
| Stateless MCP | The 2026-07-28 model with no initialize handshake and no Mcp-Session-Id; each request carries version and capabilities in _meta. |
| stdio transport | The MCP binding where a client launches the server as a subprocess and exchanges newline-delimited JSON-RPC over standard streams. |
| Step-up authorization | Requesting a wider scope set after a 403 insufficient_scope challenge, keeping previously granted scopes. |
| Streamable HTTP | The MCP HTTP binding where each message is a POST to one endpoint and replies come as JSON or a request-scoped SSE stream. |
| Tasks extension | An official MCP extension for long-running operations with polling and durable handles, moved out of core in 2026-07-28. |
| Tool | A function an MCP server offers for the model to call, with a name, description and input schema. |
| Tool annotations | Hints on a tool such as readOnlyHint and destructiveHint that tell clients how risky a call is. |
| WebMCP | A draft browser API for pages to register JavaScript tools that an in-browser agent can call. |