MCP sampling/createMessage Request and Result

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://api-evangelist.github.io/mcp/json-schema/mcp-sampling-schema.json",
  "title": "MCP sampling/createMessage Request and Result",
  "description": "Server-initiated request asking the host's LLM to generate a message. Must be approved by the user; the protocol intentionally limits server visibility into the prompt.",
  "oneOf": [
    { "$ref": "#/$defs/CreateMessageRequest" },
    { "$ref": "#/$defs/CreateMessageResult" }
  ],
  "$defs": {
    "CreateMessageRequest": {
      "type": "object",
      "required": ["jsonrpc", "id", "method", "params"],
      "properties": {
        "jsonrpc": { "const": "2.0" },
        "id": { "oneOf": [{ "type": "string" }, { "type": "integer" }] },
        "method": { "const": "sampling/createMessage" },
        "params": {
          "type": "object",
          "required": ["messages", "maxTokens"],
          "properties": {
            "messages": {
              "type": "array",
              "items": { "$ref": "#/$defs/SamplingMessage" }
            },
            "modelPreferences": {
              "type": "object",
              "properties": {
                "hints": { "type": "array", "items": { "type": "object" } },
                "costPriority": { "type": "number", "minimum": 0, "maximum": 1 },
                "speedPriority": { "type": "number", "minimum": 0, "maximum": 1 },
                "intelligencePriority": { "type": "number", "minimum": 0, "maximum": 1 }
              }
            },
            "systemPrompt": { "type": "string" },
            "includeContext": { "enum": ["none", "thisServer", "allServers"] },
            "temperature": { "type": "number" },
            "maxTokens": { "type": "integer", "minimum": 1 },
            "stopSequences": { "type": "array", "items": { "type": "string" } },
            "metadata": { "type": "object" }
          }
        }
      }
    },
    "CreateMessageResult": {
      "type": "object",
      "required": ["role", "content", "model"],
      "properties": {
        "role": { "const": "assistant" },
        "content": { "type": "object" },
        "model": { "type": "string" },
        "stopReason": {
          "enum": ["endTurn", "stopSequence", "maxTokens", "other"]
        }
      }
    },
    "SamplingMessage": {
      "type": "object",
      "required": ["role", "content"],
      "properties": {
        "role": { "enum": ["user", "assistant"] },
        "content": {
          "oneOf": [
            { "type": "object", "properties": { "type": { "const": "text" }, "text": { "type": "string" } } },
            { "type": "object", "properties": { "type": { "const": "image" }, "data": { "type": "string" }, "mimeType": { "type": "string" } } }
          ]
        }
      }
    }
  }
}