I'm passing metadat to my assistant metadata.sessionId. I want vapi to call a tool that uses this sessionId as a parameter. 100% of the time the tool function is called with a random value, how do i force it to use the sessionId from the metadata? One Example: • Call ID: 90c7ccfb-9d00-4b75-b75d-97c74822a3d6 • Timestamp: 1746309515839 • Expected Response

{
  "role": "tool_calls",
  "time": 1746309515839,
  "message": "",
  "toolCalls": [
    {
      "id": "1746309515838-9g1zeofn3",
      "type": "function",
      "function": {
        "name": "onboarding_name",
        "arguments": "{\"firstName\": \"Jason\", \"sessionId\": \"9ebd66bc-d6cd-4ffc-bee6-2a152c638892\"}"
      }
    }
  ],
  "secondsFromStart": 14.17
}

• Recieved Response:

{
  "role": "tool_calls",
  "time": 1746309515839,
  "message": "",
  "toolCalls": [
    {
      "id": "1746309515838-9g1zeofn3",
      "type": "function",
      "function": {
        "name": "onboarding_name",
        "arguments": "{\"firstName\": \"Jason\", \"sessionId\": \"789\"}"
      }
    }
  ],
  "secondsFromStart": 14.17
}

Tool Config:

{
  "id": "c51c3cbc-720c-4665-8e41-02213a910689",
  "createdAt": "2025-05-03T14:21:24.224Z",
  "updatedAt": "2025-05-03T22:01:25.388Z",
  "type": "function",
  "function": {
    "name": "onboarding_name",
    "strict": false,
    "description": "passes the user's name and sessionId to the homepage",
    "parameters": {
      "type": "object",
      "properties": {
        "firstName": {
          "description": "User's first name",
          "type": "string"
        },
        "sessionId": {
          "description": "Session identifier",
          "type": "string"
        }
      },
      "required": [
        "firstName"
      ]
    }
  },
  "messages": [
    {
      "type": "request-start",
      "content": "",
      "blocking": false
    }
  ],
  "orgId": "7d9d27d3-e3a7-4f11-b129-81f322f27766",
  "server": {
    "url": "https://mitissa.vercel.app/api/webhook",
    "headers": {}
  },
  "async": false
}

Try using the

assistantOverrides

parameter with

variableValues

when initializing your Vapi instance:

javascript
vapiInstance = vapiSDK.run({
  apiKey: apiKey,
  assistant: assistant,
  config: buttonConfig,
  assistantOverrides: {
    variableValues: {
      sessionId: "9ebd66bc-d6cd-4ffc-bee6-2a152c638892"
    }
  }
});

This explicitly passes your sessionId as a variable that can be accessed by your tool function. Source: - [Discord discussion about passing data to webhooks](https://discord.com/channels/1211482211119796234/1339495894801711186)

I applied the override but it still adds random values to the tool params

Check your assistant's configuration to ensure the variable is properly defined. Gather the Call ID and check the logs in the Vapi dashboard (logs > calls) to see how the variable is being processed:

javascript
// Also verify the variable name matches exactly in both places
console.log("Debugging sessionId variable:", {
  providedInOverrides: "9ebd66bc-d6cd-4ffc-bee6-2a152c638892",
  receivedInTool: "789" // The random value you're seeing
});

If the issue persists, contact Vapi support with your Call ID for in-depth investigation. Source: - [Discord discussion about debugging tool calls](https://discord.com/channels/1211482211119796234/1340404440892444742)

the fix was to include my variables in my prompt as so {{sessionId}}

checking if this is resolved/solved for you?

yeah its resolved now

Marking this ticket as Solved ✅