Read-only tools

[guidodecaso]

Pre-submission Checklist

• I have verified this would not be more appropriate as a feature request in a specific repository
• I have searched existing discussions to avoid duplicates

Your Idea

Would be good if MCP tool lists would include metadata about which tools are read-only and which ones are not. For example: a tool that reads all the events in a calendar is read only. A tool that creates a new event is not.

Not having this information is a step back from pure HTTP, in which some verbs are safe to retry or cache, while others are not.

Example request:

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/list"
}

Example response:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "tools": [
      {
        "name": "get_weather",
        "description": "Get current weather information for a location",
        "readOnly": true,
        "inputSchema": {
          "type": "object",
          "properties": {
            "location": {
              "type": "string",
              "description": "City name or zip code"
            }
          },
          "required": ["location"]
        }
      },
      {
        "name": "update_city_details",
        "description": "Updates the details for a city",
        "readOnly": false,
        "inputSchema": {
          "type": "object",
          "properties": {
            ...
          },
          "required": ["location"]
        }
      }

    ],
    "nextCursor": "next-page-cursor"
  }
}

For backwards compatibility, we could assume that a missing readOnly property would be treated as false. In other words, if it doubt then assume that the tool will produce a change in the world and will not be safe to retry/cache/etc...

Scope

• Protocol Specification
• SDK Features
• Documentation
• Developer Experience
• Other

[tadasant]

This is available in the spec within ToolAnnotations.

[guidodecaso]

very cool, thx. Closing