# MCP Tool

> **TL;DR.** An [MCP tool](https://modelcontextprotocol.

- **Category:** AI / Developer Tools / Infrastructure
- **Stage:** established
- **Age:** 568 days
- **Origin date:** 2024-11-25
- **First detected:** 2026-04-20
- **Canonical URL:** https://earlyterms.com/term/mcp-tool
- **Sources:** 8 primary URLs

## Definition

An [MCP tool](https://modelcontextprotocol.io/docs/concepts/tools) is one executable function exposed by an [MCP server](https://modelcontextprotocol.io/) to a language model over JSON-RPC, defined by a name, description, and JSON-Schema input shape. Tools are one of the three Model Context Protocol primitives — alongside resources and prompts — and the one models actually call.

The term travels with the [MCP specification Anthropic released on November 25, 2024](https://www.anthropic.com/news/model-context-protocol); `tools/list` and `tools/call` were protocol messages from day one. In 2026 the phrase has hardened from spec jargon into the working noun for any agent-callable capability — `get_weather`, `search_repos`, `send_message` — regardless of which MCP server ships it.

## Example

Google's [MCP Toolbox for Databases](https://github.com/googleapis/mcp-toolbox) (14.7k stars) exposes a catalog of MCP tools — `execute_sql`, `list_tables`, `describe_schema` — that Claude, Cursor, and VS Code invoke identically. [fastapi-mcp](https://github.com/tadata-org/fastapi_mcp) (11.8k stars) auto-converts FastAPI endpoints into MCP tools with auth, so a REST backend becomes agent-callable without rewriting.

## Analogy

A single button on the agent's dashboard: the MCP server is the dashboard, each tool is one button with a label and a form.

## Why it's emerging now

'MCP tool' is a compositional noun, not a coined term — it simply names one primitive inside the Model Context Protocol. What made it searchable in 2025–2026 is scale: public MCP servers passed 10,000, agents now load hundreds of tools at once, and Anthropic's November 2025 post on MCP context-strain turned 'too many MCP tools' into a first-class engineering problem.

## Related terms

- *parent:* MCP Server
- *parent:* Model Context Protocol
- *alias:* tool calling
- *related:* function calling
- *related:* MCP Resources
- *related:* MCP Prompts
- *related:* context engineering
- *related:* context rot
- *related:* context window
- *related:* agent harness
- *related:* agents.md
- *related:* managed agents

## Sources

1. [MCP Tools specification (modelcontextprotocol.io)](https://modelcontextprotocol.io/docs/concepts/tools)
2. [Anthropic — Introducing the Model Context Protocol](https://www.anthropic.com/news/model-context-protocol)
3. [Anthropic — Code execution with MCP](https://www.anthropic.com/engineering/code-execution-with-mcp)
4. [Anthropic — Writing effective tools for AI agents](https://www.anthropic.com/engineering/writing-tools-for-agents)
5. [Wikipedia — Model Context Protocol](https://en.wikipedia.org/wiki/Model_Context_Protocol)
6. [MCP Toolbox for Databases (Google)](https://github.com/googleapis/mcp-toolbox)
7. [fastapi-mcp — Expose FastAPI endpoints as MCP tools](https://github.com/tadata-org/fastapi_mcp)
8. [HN — OSS ChatGPT WebUI with MCP tools (131 pts)](https://news.ycombinator.com/item?id=46766432)

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_Generated by EarlyTerms · https://earlyterms.com/term/mcp-tool_