Skill

twilio-voice-twiml

Name: twilio-voice-twiml
Author: Twilio

build voice call logic with TwiML

Published by Twilio Updated Jul 17

Covers Python API Development Voice Node.js Twilio

Description

Build voice call logic using TwiML (Twilio Markup Language). Covers the core verbs (Say, Play, Gather, Dial, Record, Conference), generating TwiML with Python and Node.js SDKs, and a complete inbound call IVR example. Use this skill to define call behavior for inbound or outbound calls.

SKILL.md

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

Parameter	Description
`CallSid`	Unique call identifier
`From`	Caller's number
`To`	Called number
`CallStatus`	Current status
`Direction`	`inbound` or `outbound-api`

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

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