External Actions allow Vocode agents to take actions outside the realm of a phone call. In particular, Vocode agents can decide to push information to external systems via an API request, and pull information from the API response in order to:

  1. give the agent context to inform the rest of the phone call
  2. change the agent’s behavior based on the pulled information
  3. run functions/tasks outside the call

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How it Works

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Configuring an External Action with ExecuteExternalActionVocodeActionConfig

The Vocode Agent will determine after each turn of conversation if its the ideal time to interact with the External API based primarily on the configured External Action’s description and input_schema!

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Overview

  • processing_mode: We currently only support muted, which makes the agent silent while processing the request.

  • name: the name of the external action — this has no impact on the functionality of action itself.

  • description: Used by the Function Calling API to determine when to make the External Action call itself. See the description field section below for more info!

  • url: The API request is sent to this URL in the format defined below in Responding to External Action API Requests

  • input_schema: A JSON Schema for the payload to send to the External API. See the input_schema field section below for more info!

  • speak_on_send: if True, then the underlying LLM will generate a message to be spoken as the API request is being sent.

  • speak_on_receive: if True, then the agent will speak once it receives a result from the API Response. If the response does not contain an agent_message (see Response Formatting), the agent will query the LLM for the message to speak.

  • signature_secret: a base64 encoded string to enable request validation, see the Signature Validation section below for more info

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input_schema Field

The input_schema field is a JSON Schema form the payload to send to the External API.

For example, in the Meeting Assistant Example below we formed the following JSON schema:

{
  "type": "object",
  "properties": {
    "length": {
      "type": "string",
      "enum": ["30m", "1hr"]
    },
    "time": {
      "type": "string",
      "pattern": "^d{2}:d0[ap]m$"
    }
  }
}

This is stating the External API is expecting:

  • Two fields
    • length (string): either “30m” or “1hr”
    • time (string): a regex pattern defining a time ending in a zero with am/pm on the end ie: 10:30am

💡 Note

If you’re noticing that this looks very familiar to OpenAI function calling, it is! Vocode treats OpenAI Function Calling as a first-class standard when the agent uses an OpenAI LLM.

The lone difference is that the top level input_schema JSON schema must be an object - this is so we can use JSON to send over parameters to the user’s API.

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description Field

The description is best used to descibe your External Action’s purpose. As its passed through directly to the LLM, its the best way to convey instructions to the underlying Vocode Agent.

For example, in the Meeting Assistant Example below we want to book a meeting for 30 minutes to an hour so we set the description as Book a meeting for a 30 minute or 1 hour call.

💡 Note

The description field is passed through and heavily affects how functions are triggered and queried, so we recommend treating it similar to prompting for an LLM!

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Responding to External Action API Requests

Once an External Action has been created, the Vocode Agent will issue API requests to the defined url during the course of a phone call based on the configuration noted above The Vocode API will wait a maximum of 10 seconds before timing out the request.

In particular, Vocode will issue a POST request to url with a JSON payload that specifically matches input_schema. Using the Meeting Assistant Example below, the request will contain:

POST url HTTP/1.1
Accept: application/json
Content-Type: application/json
x-vocode-signature: <encoded_signature>

{
  "payload": {
    "length": "30m",
    "time": "10:30am"
  }
}

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Signature Validation

A cryptographically signed signature of the request body and a randomly generated byte hash is included as a header (under x-vocode-signature) in the outbound request, so the receiving API can validate the identity of the incoming request. The signature secret is used to sign the request and ensure the validity of the x-vocode-signature field, and therefore must be securely managed.

This should be set as a base64-encoded string and we recommend a longer length as well, using the following snippet as an example:

import os
import base64

signature_secret = base64.b64encode(os.urandom(32)).decode()

Use the following code snippet to check the signature in an inbound request:

import base64
import hashlib
import hmac

async def test_requester_encodes_signature(
  request_signature_value: str, signature_secret: str, payload: dict
):
    """
    Asynchronous function to check if the request signature is encoded correctly.

    Args:
        request_signature_value (str): The request signature to be decoded.
        signature_secret (str): The secret for the action (make sure this is stored securely).
        payload (dict): The payload to be used for digest calculation.

    Returns:
        None
    """
    signature_secret_as_bytes = base64.b64decode(signature_secret)
    decoded_digest = base64.b64decode(request_signature_value)
    calculated_digest = hmac.new(signature_secret_as_bytes, json.dumps(payload).encode(), hashlib.sha256).digest()
    assert hmac.compare_digest(decoded_digest, calculated_digest) is True

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Response Formatting

Vocode expects responses from the user’s API in JSON in the following format:

Response {
  result: Any
  agent_message: Optional[str] = None
}
  • result is a payload containing the result of the action on the user’s side, and can be in any format
  • agent_message optionally contains a message that will be synthesized into audio and sent back to the phone call. Note this means the LLM will not be queried to send a message (see Configuring the External Action above for more info)

In the Meeting Assistant Example below, the user’s API could return back a JSON response that looks like:

{
  "result": {
    "success": true
  },
  "agent_message": "I've set up a calendar appointment at 10:30am tomorrow for 30 minutes"
}

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EA Local Response Server Example:

The following is an example of a quick start to enable testing external actions locally.

Running fastapi dev app.py will run the server @ http://127.0.0.1:8000 and can be used for external actions locally!

import asyncio
import base64
import hashlib
import hmac
import json
import time

from fastapi import FastAPI, HTTPException, Request, status
from pydantic import BaseModel

app = FastAPI()

action_secret = ""


def is_signature_valid(request: Request, json_payload: dict):
    signature_secret_as_bytes = base64.b64decode(action_secret)
    decoded_digest = base64.b64decode(request.headers.get("x-vocode-signature"))
    calculated_digest = hmac.new(
        signature_secret_as_bytes, json.dumps(json_payload).encode(), hashlib.sha256
    ).digest()
    return hmac.compare_digest(decoded_digest, calculated_digest)


@app.post("/external_action")
def update_item(request: Request):
    json_payload = asyncio.run(request.json())
    print(json_payload)
    if not is_signature_valid(request, json_payload):
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Signature verification failed for payload",
        )
    time.sleep(3)
    return {
        "result": {"success": True},
    }

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Meeting Assistant Example

This is an example of how to create an action config which will attempt to book a meeting for 30 minutes or an hour at any time ending in a zero (ie 10:30am is okay but 10:35am is not)

Python
import json
import base64
import os

from vocode.streaming.action.execute_external_action import (
    ExecuteExternalAction,
    ExecuteExternalActionVocodeActionConfig,
)

ACTION_INPUT_SCHEMA = {
    "type": "object",
    "properties": {
        "length": {
            "type": "string",
            "enum": ["30m", "1hr"],
        },
        "time": {
            "type": "string",
            "pattern": "^\d{2}:\d0[ap]m$",
        },
    },
}

action_config = ExecuteExternalActionVocodeActionConfig(
    name = "Meeting_Booking_Assistant",
    description = "Book a meeting for a 30 minute or 1 hour call.",
    url = "http://example.com/booking",
    speak_on_send = True,
    speak_on_receive = True,
    input_schema = json.dumps(ACTION_INPUT_SCHEMA),
    signature_secret = base64.b64encode(os.urandom(32)).decode(),
)

See Action Agents for an example of how to use this action config with an agent in a conversation. Note that you do not need to create a custom action factory, since DefaultActionFactory already supports external actions.

Action TriggersConversation Mechanics