twilio-voice-twiml

Imported from openai/plugins (plugins/twilio-developer-kit/skills/twilio-voice-twiml/SKILL.md). Install upstream with npx skills add openai/plugins --skill twilio-voice-twiml. Copyright stays with the author.

Overview

TwiML is XML that Twilio executes during a call. Your server returns a TwiML document in response to a Twilio webhook POST, and Twilio executes it.

Caller → Twilio → POST to your webhook → Your server returns TwiML → Twilio executes it

Prerequisites

• Twilio account with a voice-capable phone number — New to Twilio? See twilio-account-setup
• Webhook endpoint returning TwiML with Content-Type: text/xml
• SDK (for programmatic generation): pip install twilio / npm install twilio

Quickstart

A minimal inbound call handler that greets the caller and presents a menu:

Python (Flask)

from flask import Flask, request
from twilio.twiml.voice_response import VoiceResponse

app = Flask(__name__)

@app.route("/voice", methods=["POST"])
def handle_call():
    response = VoiceResponse()
    gather = response.gather(num_digits=1, action="/menu-choice")
    gather.say("Welcome to Acme. Press 1 for sales, 2 for support.")
    response.redirect("/voice")  # Loop if no input
    return str(response)

@app.route("/menu-choice", methods=["POST"])
def menu_choice():
    digit = request.form.get("Digits")
    response = VoiceResponse()
    if digit == "1":
        response.dial("+15551234567")
    elif digit == "2":
        response.say("Connecting to support.")
        response.dial("+15559876543")
    else:
        response.say("Invalid option.")
        response.redirect("/voice")
    return str(response)

Node.js (Express)

const { VoiceResponse } = require("twilio").twiml;

app.post("/voice", (req, res) => {
    const response = new VoiceResponse();
    const gather = response.gather({ numDigits: 1, action: "/menu-choice" });
    gather.say("Welcome. Press 1 for sales, 2 for support.");
    response.redirect("/voice");
    res.type("text/xml").send(response.toString());
});

app.post("/menu-choice", (req, res) => {
    const digit = req.body.Digits;
    const response = new VoiceResponse();
    if (digit === "1") response.dial("+15551234567");
    else response.say("Invalid option.").redirect("/voice");
    res.type("text/xml").send(response.toString());
});

Core Verbs

Say — Text-to-speech

Python

from twilio.twiml.voice_response import VoiceResponse

response = VoiceResponse()
response.say("Your appointment is confirmed.", voice="alice", language="en-US")

Node.js

const { VoiceResponse } = require("twilio").twiml;
const response = new VoiceResponse();
response.say({ voice: "alice", language: "en-US" }, "Your appointment is confirmed.");

Voices: alice (default), man, woman, or Polly/Google TTS (e.g. Polly.Joanna).

Gather — Collect keypad input or speech

Python

response = VoiceResponse()
gather = response.gather(num_digits=1, action="/handle-input", method="POST")
gather.say("Press 1 for sales, press 2 for support.")
response.say("We did not receive your input.")  # Fallback if no input

Node.js

const gather = response.gather({ numDigits: 1, action: "/handle-input", method: "POST" });
gather.say("Press 1 for sales, press 2 for support.");
response.say("We did not receive your input.");

Twilio POSTs collected digits to action as Digits parameter.

Play — Play an audio file

Python

response = VoiceResponse()
response.play("https://example.com/audio/greeting.mp3")

Node.js

const response = new VoiceResponse();
response.play("https://example.com/audio/greeting.mp3");

Supported formats: MP3, WAV. URL must be publicly accessible.

Dial — Connect to another number

Python

from twilio.twiml.voice_response import Dial

response = VoiceResponse()
dial = Dial(action="/dial-complete")
dial.number("+15558675310")
response.append(dial)

Node.js

const dial = response.dial({ action: "/dial-complete" });
dial.number("+15558675310");

Record — Capture caller audio

Python

response = VoiceResponse()
response.say("Leave a message after the beep.")
response.record(
    action="/recording-complete",
    max_length=60,
    transcribe=True,
    transcribe_callback="/transcription-ready"
)

Node.js

const response = new VoiceResponse();
response.say("Leave a message after the beep.");
response.record({
    action: "/recording-complete",
    maxLength: 60,
    transcribe: true,
    transcribeCallback: "/transcription-ready",
});

Voicemail — Record a message when no one answers

Use <Dial> with action URL + <Record> in the action handler. When the dial times out or the callee is busy, the action URL serves TwiML with <Record>.

Python

# Primary TwiML — try to connect the call
response = VoiceResponse()
dial = Dial(action="/voicemail", timeout=20)  # 20 seconds before voicemail
dial.number("+15558675310")
response.append(dial)

# /voicemail handler — plays if no answer
def voicemail_handler(request):
    response = VoiceResponse()
    response.say("We missed your call. Please leave a message after the beep.")
    response.record(
        action="/recording-complete",
        max_length=120,
        transcribe=True,
        transcribe_callback="/transcription-ready",
        play_beep=True
    )
    response.say("We didn't receive a recording. Goodbye.")
    return str(response)

Node.js

// Primary TwiML — try to connect the call
const response = new VoiceResponse();
const dial = response.dial({ action: "/voicemail", timeout: 20 });
dial.number("+15558675310");

// /voicemail handler — plays if no answer
app.post("/voicemail", (req, res) => {
    const response = new VoiceResponse();
    response.say("We missed your call. Please leave a message after the beep.");
    response.record({
        action: "/recording-complete",
        maxLength: 120,
        transcribe: true,
        transcribeCallback: "/transcription-ready",
        playBeep: true,
    });
    response.say("We didn't receive a recording. Goodbye.");
    res.type("text/xml").send(response.toString());
});

Important: <Record> captures the caller only (voicemail-style). It is NOT for recording two-party calls — see twilio-call-recordings for that.

Conference — Multi-party calls

Python

response = VoiceResponse()
dial = response.dial()
dial.conference(
    "Daily Standup",
    start_conference_on_enter=True,
    end_conference_on_exit=True
)

Node.js

const response = new VoiceResponse();
const dial = response.dial();
dial.conference("Daily Standup", {
    startConferenceOnEnter: true,
    endConferenceOnExit: true,
});

Pay — PCI-compliant payment collection

Critical warnings:

• Pay Connectors are Console-only — there is no REST API to create or manage connectors. Set up in Console > Voice > Pay Connectors before coding.
• PCI Mode is IRREVERSIBLE once enabled on an account. Use a dedicated sub-account for payment calls.

Python

response = VoiceResponse()
response.say("We'll now collect your payment.")
pay = Pay(
    payment_connector="stripe_connector",  # Name from Console setup
    charge_amount="49.99",
    currency="usd",
    action="/payment-complete",
    status_callback="/payment-status"
)
response.append(pay)

Node.js

const response = new VoiceResponse();
response.say("We'll now collect your payment.");
response.pay({
    paymentConnector: "stripe_connector",
    chargeAmount: "49.99",
    currency: "usd",
    action: "/payment-complete",
    statusCallback: "/payment-status",
});

Supported processors: Stripe, Braintree, CardConnect. Card data routes directly to the processor — never touches your server.

Production Deployment

Webhook Hosting

For production, do NOT use ngrok. Deploy your TwiML server with HTTPS:

• Requirement: Public HTTPS URL, responds within 15 seconds, returns Content-Type: text/xml
• Options: Cloud Run, AWS Lambda + API Gateway, Railway, Render — any service with TLS and auto-scaling
• Fallback URL: Configure in Console (Phone Numbers > Active Numbers > select number) for when your primary server is unreachable

State Between TwiML Requests

Each webhook request is stateless. To maintain conversation state across interactions:

• URL query params: Pass state in action URLs — /next-step?language=es&dept=sales
• Session store: Use Redis or a database keyed by CallSid
• Do NOT use in-memory state — your server may scale to multiple instances

Monitoring

• Status callbacks: Track call lifecycle events (statusCallback on the call or number config)
• Voice Insights: Automatic quality metrics per call (Console > Monitor > Insights)
• Debugger: Console > Monitor > Errors for TwiML parsing failures and webhook timeouts
• Fallback URLs: Always configure a fallback TwiML URL — serves a graceful message if your primary endpoint fails

Webhook Request Parameters

CANNOT

• Cannot return TwiML without correct content type — Must use Content-Type: text/xml
• Cannot exceed 15-second webhook response time — Twilio times out and falls back
• Cannot exceed 4,096 characters in <Say> verb — Split longer text across multiple <Say> elements
• Cannot create Pay Connectors via API — Pay Connectors are Console-only (Console > Voice > Pay Connectors). No REST API exists for connector management.
• Cannot reverse PCI Mode — Once enabled on an account, PCI Mode is permanent and account-wide. Use a dedicated sub-account for payment calls.
• Cannot use <Record> for two-party call recording — <Record> captures the caller only (voicemail-style). For dual-channel recording of both parties, use record=True on calls.create() or the Recordings API.

Next Steps

• Place outbound calls (AMD, conferencing): twilio-voice-outbound-calls
• AI voice agents with real-time speech/LLM: twilio-voice-conversation-relay