> ## Documentation Index
> Fetch the complete documentation index at: https://prefab.prefect.io/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# ToolCall

> JSON Schema for the ToolCall action.

Call an MCP server tool via `app.callServerTool()`.

```json theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
{
  "type": "object",
  "properties": {
    "action": {
      "const": "toolCall",
      "default": "toolCall",
      "type": "string"
    },
    "tool": {
      "description": "Name of the server tool to call",
      "type": "string"
    },
    "arguments": {
      "additionalProperties": true,
      "description": "Arguments to pass. Supports {{ key }} interpolation.",
      "type": "object"
    }
  },
  "required": [
    "action",
    "tool"
  ]
}
```