02 · MCP Glossary¶
A quick cheat-sheet of every term you'll bump into.
| Term | Meaning |
|---|---|
| MCP | Model Context Protocol. Open standard for connecting AI apps to tools and data. "USB-C for AI." |
| Host | The AI application you use (Claude Desktop, VS Code, Cursor, ChatGPT...). |
| Client | Component inside a host; one per server. Maintains the connection to the server. |
| Server | Your program. Exposes tools, resources, and prompts. |
| Tool | A function the AI model can call to take an action. (Model-controlled.) |
| Resource | Read-only data (file, schema, doc) the app loads as context. (Application-controlled.) |
| Prompt | A reusable instruction template invoked by the user. |
| JSON-RPC 2.0 | The message protocol MCP is built on: requests, responses, notifications. |
| Data layer | The "what" of MCP: the JSON-RPC messages and primitives. |
| Transport layer | The "how": how messages travel. |
| stdio transport | Local transport. Client spawns server as a subprocess; talks over stdin/stdout. |
| Streamable HTTP | Remote transport. HTTP POST + Server-Sent Events; supports auth. |
| Discovery | server/discover — the client asks the server what it supports and which versions it speaks. |
| Capabilities | The features a server/client supports (tools, resources, prompts, ...). |
tools/list |
Discover available tools. |
tools/call |
Execute a tool with arguments. |
resources/list |
Discover available resources. |
resources/read |
Fetch a resource's content by URI. |
prompts/list |
Discover available prompts. |
prompts/get |
Fetch a prompt's template and arguments. |
| JSON Schema | The format used to describe a tool's expected inputs. |
| Input schema | The inputSchema on a tool — auto-generated from Python type hints + docstrings. |
| MIME type | Declares resource content type (e.g. text/markdown, application/json). |
| Notification | A message with no response expected (e.g. "tools changed"). |
| Stateless | Each request stands alone; carries version + capabilities in _meta. |
| Protocol version | The negotiated version string (e.g. 2026-07-28). |
| MCP Inspector | Official web UI for poking at your server and watching the JSON-RPC traffic. |
mcp dev |
CLI command that launches the Inspector pointed at your server. |
| Elicitation | Client primitive: server can ask the user for more input. |
| Sampling | (deprecated in 2026-07-28) server asks the client's LLM for a completion. |