Model Context Protocol (MCP) · Schema

MCP Tool

A callable function exposed by an MCP server. Tools have a JSON Schema 2020-12 input schema and are invoked via tools/call.

Model Context ProtocolMCPAI AgentsToolsResourcesPromptsJSON-RPCAnthropicStandardsTopic

Properties

Name	Type	Description
name	string	Stable identifier used in tools/call.
title	string	Human-readable display name.
description	string	Natural-language description of what the tool does. Untrusted unless the server is trusted.
inputSchema	object	JSON Schema 2020-12 describing the tool's input parameters.
outputSchema	object	Optional JSON Schema describing structured tool output.
annotations	object	Optional behavioral hints for clients (e.g. readOnlyHint, destructiveHint, idempotentHint, openWorldHint).
icons	array
_meta	object

View JSON Schema on GitHub

JSON Schema

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://api-evangelist.github.io/mcp/json-schema/mcp-tool-schema.json",
  "title": "MCP Tool",
  "description": "A callable function exposed by an MCP server. Tools have a JSON Schema 2020-12 input schema and are invoked via tools/call.",
  "type": "object",
  "required": ["name", "inputSchema"],
  "properties": {
    "name": {
      "type": "string",
      "description": "Stable identifier used in tools/call."
    },
    "title": {
      "type": "string",
      "description": "Human-readable display name."
    },
    "description": {
      "type": "string",
      "description": "Natural-language description of what the tool does. Untrusted unless the server is trusted."
    },
    "inputSchema": {
      "type": "object",
      "description": "JSON Schema 2020-12 describing the tool's input parameters."
    },
    "outputSchema": {
      "type": "object",
      "description": "Optional JSON Schema describing structured tool output."
    },
    "annotations": {
      "type": "object",
      "description": "Optional behavioral hints for clients (e.g. readOnlyHint, destructiveHint, idempotentHint, openWorldHint).",
      "properties": {
        "title": { "type": "string" },
        "readOnlyHint": { "type": "boolean" },
        "destructiveHint": { "type": "boolean" },
        "idempotentHint": { "type": "boolean" },
        "openWorldHint": { "type": "boolean" }
      }
    },
    "icons": {
      "type": "array",
      "items": { "type": "object" }
    },
    "_meta": { "type": "object" }
  },
  "additionalProperties": false
}