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# Twilio Documentation

> Reference documentation for all Twilio products. Code snippets, tutorials, and sample apps for common use cases and communications solutions.

## Authy: 2FA and Passwordless Login

* [Authy: 2FA and Passwordless Login](/docs/authy.md): Easily add two-factor authentication and passwordless logins via API or with our SDKs. Protect logins and step-up transactions with SMS, Voice, PushAuthentications, and TOTP through a simple API. Reduce fraud and increase user trust - follow these guides, reference docs, and tutorials.

## Building with AI

* [Building with AI](/docs/ai.md): Integrate Twilio APIs with AI coding agents using MCP servers, or use AI-powered communication products. Build faster with intelligent tools.
* [Twilio MCP server](/docs/ai/mcp.md): Connect AI coding agents to Twilio's API documentation with the Model Context Protocol server. Search over 1,800 endpoints and retrieve schemas on demand.
* [Twilio Skills for AI coding agents](/docs/ai/skills.md): Install Twilio Skills to teach AI coding agents which Twilio products to use, proven architecture patterns, and how to avoid common mistakes. Works with Claude Code, Cursor, Codex, and other Agent Skills-compatible tools.

## Conversation Intelligence (classic)

* [AI Nutrition Fact Labels](/docs/conversation-intelligence-classic/ai-nutrition-fact-labels.md): View AI Nutrition Fact Labels for the Twilio Conversation Intelligence (classic) Base Models.
* [Conversation Intelligence (classic) API Overview](/docs/conversation-intelligence-classic/api.md): Learn how to use the Twilio Conversation Intelligence (classic) API to analyze and extract actionable insights from conversations using AI and machine learning.
* [Conversation Intelligence (classic) - Service Resource](/docs/conversation-intelligence-classic/api/service-resource.md): Learn how to create, fetch, list, update, and delete a Service with Twilio's Conversation Intelligence (classic) API. Access detailed API reference and code samples.
* [Conversation Intelligence (classic) - Transcript Resource](/docs/conversation-intelligence-classic/api/transcript-resource.md): API reference for the Conversation Intelligence (classic) API Transcript resource, which represents a voice conversation that has automatically been converted to text through Twilio's transcription engine.
* [Conversation Intelligence (classic) - Transcript Sentence Subresource](/docs/conversation-intelligence-classic/api/transcript-sentence-subresource.md): Full API reference for the Transcript Sentence subresource in the Twilio Conversation Intelligence (classic) API. Sample code shows how to list the Sentences of a Transcript.
* [Conversation Relay integration for AI agent observability](/docs/conversation-intelligence-classic/conversation-relay-integration.md): Built-in AI agent observability with AI-powered language analysis
* [Customize Your Conversation Intelligence (classic) Configuration](/docs/conversation-intelligence-classic/customize.md): Learn more advanced concepts and implementations for Conversation Intelligence (classic), including using transcript sources outside of Twilio.
* [Generative Custom Operators](/docs/conversation-intelligence-classic/generative-custom-operators.md): LLM-backed Language Operators provide flexible and powerful conversational analysis supporting a wide range of sophisticated natural language understanding use cases.
* [Conversation Intelligence (classic)](/docs/conversation-intelligence-classic.md): Conversation Intelligence (classic) turns the content of your voice calls and messages into structured information to help you enrich customer profiles, optimize lead generation campaigns, address compliance issues, and assess agent performance across every conversation.
* [Language Operators](/docs/conversation-intelligence-classic/language-operators.md): Discover AI-powered Language Operators to analyze conversations and gain valuable insights. Learn about Pre-built and Custom Operators.
* [Conversation Intelligence (classic) onboarding guide](/docs/conversation-intelligence-classic/onboarding.md): Learn the basic concepts and how to configure Conversation Intelligence (classic) for AI insights from conversations. Set up via API or Twilio Console for seamless integration.
* [Pre-built Language Operators](/docs/conversation-intelligence-classic/pre-built-operators.md): Explore Pre-built Language Operators for Twilio Conversation Intelligence (classic), designed to classify, summarize, and extract key insights from conversation transcripts.

## Elastic SIP Trunking

* [Emergency Calling for SIP Trunking API](/docs/sip-trunking/api/emergency-calling.md): Twilio's Emergency Address registration enables emergency call routing to Public Safety Answering Points (PSAPs) in the US, Canada and the UK.
* [Elastic SIP Trunking REST API Reference](/docs/sip-trunking/api.md): Learn how to get started with Twilio Elastic SIP Trunking and view the REST API reference.
* [PhoneNumber Resource](/docs/sip-trunking/api/phonenumber-resource.md): Full API reference for the SIP Trunking PhoneNumber resource in the Twilio API. Learn how to create, read (list), and delete PhoneNumbers for SIP Trunks.
* [Trunk Resource](/docs/sip-trunking/api/trunk-resource.md): Full API reference for the SIP Trunking Trunk resource in the Twilio API. Learn how to create, read (list), and delete SIP Trunks.
* [Call Transfer via SIP REFER](/docs/sip-trunking/call-transfer.md): Learn how to transfer an active call with Twilio Elastic SIP Trunking using SIP REFER, including call flow, caller ID, call logs, and pricing details.
* [Elastic SIP Trunking Codecs](/docs/sip-trunking/codecs.md): Learn about supported codecs for Elastic SIP Trunking, including origination, termination, and codec priority.
* [Configure your Trunk using Twilio Interconnect](/docs/sip-trunking/configure-with-interconnect.md): Configure your SIP Trunk with Twilio Interconnect, allowing you to connect your SIP infrastructure using a private connection to an Elastic SIP Trunk.
* [Calls per Second (CPS) — Trunking Termination](/docs/sip-trunking/cps-trunk-termination.md): Learn about trunk-level Calls Per Second (CPS), parent account CPS, and debugger alerts for CPS limits.
* [Emergency Calling for SIP Trunking](/docs/sip-trunking/emergency-calling.md): Enable and configure Twilio's Emergency Calling, enabling emergency call routing to Public Safety Answering Points using Elastic SIP Trunking.
* [Extended Call Duration](/docs/sip-trunking/extended-call-duration.md): Extend the maximum call duration on Twilio Elastic SIP Trunking calls from 4 hours to 24 hours so your business can support conversations that run longer.
* [Elastic SIP Trunking](/docs/sip-trunking.md): Global pay-as-you-go connectivity for VoIP infrastructure with Twilio's Elastic SIP Trunking. Learn how to configure, troubleshoot, and connect your SBC or PBX SIP infrastructure to a Twilio Elastic SIP Trunk with our API reference documentation, tutorials, and usage guides.
* [IP Addresses for Elastic SIP Trunking Services](/docs/sip-trunking/ip-addresses.md): A complete list of Twilio's Gateway IP address ranges and ports, required for SIP signaling and RTP media traffic when using Elastic SIP Trunking.
* [Elastic SIP Trunking Configuration Guides](/docs/sip-trunking/sample-configuration.md): Use these Configuration Guides to help you connect your SIP Infrastructure (IP-PBX, SBC, etc) to a Twilio Elastic SIP Trunk.
* [Twilio SIP Trunking Scale and Limits](/docs/sip-trunking/scale-and-limits.md): This guide outlines the SIP Trunking limits you should be aware of when building with Twilio for standard accounts and when working with trial accounts.
* [SIP Header Manipulation](/docs/sip-trunking/sip-header-manipulation.md): Use SIP Header Manipulation to automatically modify phone numbers and user fields in SIP INVITE requests for Twilio Elastic SIP Trunking termination and origination calls.
* [Elastic SIP Trunking — Solution Blueprints](/docs/sip-trunking/solution-blueprints.md): Solution blueprints for your Twilio Elastic SIP Trunk including a list of contact centers, unified communications, and session border controllers.
* [Troubleshooting your Trunk](/docs/sip-trunking/troubleshooting.md): Troubleshoot your SIP Trunk, use the Twilio debugger, and explore common issues and possible solutions around SIP termination, origination, and audio issues.
* [Test your Elastic SIP Trunk](/docs/sip-trunking/trunk-verification.md): Read how to test your SIP Trunk for termination, origination, and emergency calling, as well as how to diagnose common problems.
* [Configure a 3CX PBX to use Twilio SIP Trunking](/docs/sip-trunking/trunking-3cx-pbx.md): Connect a 3CX PBX to Twilio Elastic SIP Trunking. Configure termination, origination, phone numbers, dialing routes, DID extensions, and emergency calling.
* [Protect your account with Voice Dialing Geographic Permissions](/docs/sip-trunking/voice-dialing-geographic-permissions.md): Protect your account with Voice Dialing Geographic Permissions - prevent IRSF toll-fraud

## Event Streams

* [Event Streams](/docs/events.md): Learn what you can do with Event Streams, an API that allows you to tap into a unified stream of every interaction sent or received on Twilio's network.

## Flex

* [Core concepts: Chat and Messaging](/docs/flex/admin-guide/core-concepts/chat-and-messaging.md): Understand how chat and messaging works within Flex.
* [Core concepts: Conversations](/docs/flex/admin-guide/core-concepts/conversations.md): Explore Flex Conversations, a feature supporting various asynchronous channels for both inbound and outbound communications using Flex UI 2.x.x and the Interactions API.
* [Core concepts: Flex UI](/docs/flex/admin-guide/core-concepts/flex-ui.md): Learn the core concepts and structure of Twilio Flex UI, including different user views, settings, SSO, themes, and plugins.
* [Core concepts](/docs/flex/admin-guide/core-concepts.md): Explore key concepts and building blocks for Twilio Flex.
* [Core concepts introduction](/docs/flex/admin-guide/core-concepts/introduction.md): This introduces Flex administrators to core concepts and products that Flex leverages to build your contact center.
* [Core concepts: Numbers](/docs/flex/admin-guide/core-concepts/numbers.md): This core concepts guide covers the various number types available to your Flex applications and includes provisioning and porting numbers.
* [Core concepts: Routing](/docs/flex/admin-guide/core-concepts/routing.md): Learn how Flex uses Taskrouter to route tasks to workers in your contact center workspace.
* [Core concepts: Studio Flows, Functions, Assets, TwiML](/docs/flex/admin-guide/core-concepts/studio-flows-functions-assets-twiml.md): Learn about the relationship of Studio Flows, REST API v2, Functions & Assets, and TwiML for Voice and SMS with Twilio Flex.
* [Core concepts: Voice](/docs/flex/admin-guide/core-concepts/voice.md): Learn about Flex voice features, including conferencing, secure payment options, and access to real-time audio streams.
* [Manage Flex Mobile (public beta)](/docs/flex/admin-guide/flex-mobile.md): Flex Mobile is a pre-built mobile app you can add to your existing Flex instance with no additional development effort.
* [Integrate Flex with Alvaria WFM](/docs/flex/admin-guide/integrations/alvaria.md): Learn how to integrate Alvaria Workforce Management with Twilio Flex for efficient contact center operations. Alvaria WFM enables you to efficiently forecast staff scheduling, schedule individual agents, and monitor schedule adherence.
* [Integrate Flex with Calabrio ONE WFM](/docs/flex/admin-guide/integrations/calabrio.md): Learn how Twilio Flex integrates with Calabrio ONE and how the workforce optimization solution can enhance contact center planning and operations.
* [Integrate Flex with Glance Cobrowse](/docs/flex/admin-guide/integrations/glance.md): Learn how to integrate Twilio Flex with Glance Cobrowse. This integration enables agents to launch a Cobrowse session to instantly join customers in viewing your app or website.
* [Google Dialogflow CX integration in Flex for virtual agents](/docs/flex/admin-guide/integrations/google-dialogflow-cx-native-integration.md): You can use Google Dialogflow CX Virtual Agent in Flex to handle incoming calls and conversations and route them to a live agent.
* [Integrate Flex with Lionbridge Language Cloud](/docs/flex/admin-guide/integrations/lionbridge-language-cloud.md): Explore Lionbridge Language Cloud for real-time translation in over 110 languages. Lionbridge Language Cloud is a real-time language translation solution that enables your agents and customers to each send and receive messages in their own native languages.
* [Integrate Mindful Feedback with Flex](/docs/flex/admin-guide/integrations/mindful-feedback.md): Explore Mindful Feedback, a tool that automatically collects customer feedback after any Flex interaction. View customer feedback within Flex UI on the integrated real-time reporting dashboard available for agents, supervisors and managers.
* [Integrate the Mindful platform With Flex](/docs/flex/admin-guide/integrations/mindful.md): Integrate Flex and Mindful for efficient customer callbacks. Learn to set up a SIP domain and trunk and to configure return call priority.
* [Integrate Flex with Puzzel WFM](/docs/flex/admin-guide/integrations/puzzel-wfm.md): Learn how to integrate Puzzel WFM with Twilio Flex. Puzzel WFM provides a simple, cloud-based platform that enables forecasting, scheduling, and adherence monitoring for your Twilio Flex workforce.
* [Set up Salesforce Partner Contact Center BYOC CCaaS with Twilio SMS and WhatsApp Channels](/docs/flex/admin-guide/integrations/salesforce-byoccaas.md): Learn how to configure Salesforce Bring Your Own Channel for CCaaS (BYOC CCaaS) with Twilio SMS and WhatsApp messaging channels.
* [Set up Salesforce Partner Contact Center with Twilio](/docs/flex/admin-guide/integrations/salesforce-service-cloud-voice.md): Learn how to integrate Salesforce Partner Contact Center to use Twilio as the Partner Telephony Provider.
* [Manage Flex-Salesforce call flows](/docs/flex/admin-guide/integrations/salesforce/call-flows.md): Learn how to accept incoming calls from new and existing contacts and make outgoing calls from your Flex-Salesforce integration.
* [Customize your Flex-Salesforce Integration](/docs/flex/admin-guide/integrations/salesforce/customize.md): Learn how to customize your Flex-Salesforce integration experience and call flows.
* [Integrate Flex with Salesforce](/docs/flex/admin-guide/integrations/salesforce.md): Use the Flex and Salesforce consoles to integrate your call center with Salesforce.
* [Upgrade Guide for Flex-Salesforce](/docs/flex/admin-guide/integrations/salesforce/upgrade-guide.md): Migrate your Flex-Salesforce Integration to use Native Outbound Dialing. Native Outbound Dialing enables you to take advantage of the increased stability and scale of the Flex platform and to gain access to additional features as they become available.
* [Integrate Flex with Spoke Phone (UCaaS)](/docs/flex/admin-guide/integrations/spoke-phone-ucaas.md): Explore Spoke Phone, a Unified Communications solution integrated with Twilio and Flex. Spoke Phone can serve as a full PBX replacement, enhancing connectivity.
* [Integrate Flex with Veridas Voice Biometrics](/docs/flex/admin-guide/integrations/veridas-voice-biometrics.md): Explore Veridas Voice Biometrics for a digital authentication solution. Validate the identity of your customers with just 3 seconds of their voice, in any language, and without the need of making them repeat any given sentence.
* [Manage Flex-Zendesk Call Flows](/docs/flex/admin-guide/integrations/zendesk/call-flows.md): Manage incoming and outgoing call flows in your Twilio Flex-Zendesk integration, including screen pop, interaction logging, custom tags, and click-to-dial.
* [Customize your Flex-Zendesk Integration](/docs/flex/admin-guide/integrations/zendesk/customize.md): Learn how to customize your Flex-Zendesk integration experience and call flows.
* [Integrate Flex with Zendesk](/docs/flex/admin-guide/integrations/zendesk.md): Use Twilio Flex and Zendesk together to offer an omnichannel and personalised experience to your Customers
* [Flex-Zendesk integration release notes](/docs/flex/admin-guide/integrations/zendesk/release-notes.md): Release notes for the Twilio Flex-Zendesk integration, covering added features, fixes, and changes across each plugin version.
* [Upgrade Guide for Flex-Zendesk](/docs/flex/admin-guide/integrations/zendesk/upgrade-guide.md): Upgrade your Flex-Zendesk integration to use Native Outbound Dialing.
* [Set up your Twilio Flex instance](/docs/flex/admin-guide/setup/account-creation.md): Sign up for Twilio and set up a cloud-hosted Twilio Flex contact center instance in minutes, then test the sample voice, SMS, and chat experience.
* [Alerts for contact center metrics in Flex (public beta)](/docs/flex/admin-guide/setup/alerts/alerts-contact-center-metrics.md): Configure alerts and notifications for real-time contact center metrics in Twilio Flex, including thresholds, webhooks, email, and browser push.
* [Configure pre-agent workflow with Studio](/docs/flex/admin-guide/setup/configure-pre-agent-workflow-with-studio.md): Use Twilio Studio to build pre-agent workflows for Flex, including IVR menus, chatbots, call deflection, and intelligent routing with Unified Profiles.
* [Manage Twilio Console users](/docs/flex/admin-guide/setup/console-users.md): Add and modify Flex users with administrator, developer, billing manager, or support roles in the Twilio Console.
* [Send Application-to-Person SMS in the US](/docs/flex/admin-guide/setup/conversations/a2p-10dlc.md): Register for an A2P use case, create a messaging service, and associate your A2P phone numbers with Flex Conversations.
* [Subscribe to Interactions events](/docs/flex/admin-guide/setup/conversati