Phone call testing

Retell AI

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📞 Build, test, deploy, and monitor AI phone agents.

Introduction

Deploy your first phone agent in 5 minutes.

Build your first phone agent in 5 minutes

Learn how to use Retell's Node.js and Python SDKs

SDKs

Set language for your agent

Testing Overview

A step by step guide to buy a number from Retell

Purchase phone number

Setup versioning for agents

A step by step guide to create a web call with agent using frontend Web SDK

Connect to web call

Understand the constraints and limitations of the agents.

Understand concurrency & limits

Monitor calls via dashboard

Discover how Retell AI ensures 99.9% uptime with enterprise-grade infrastructure, proactive monitoring, and fallback mechanisms. Learn about our reliability strategy, resilience features, and support system

Reliability Overview

Workspace

Account

Audio Basics

Partner Program

Affiliate Program

Create Phone Call

Create Web Call

Get Call

List Calls

Update metadata and sensitive data storage settings for an existing call

Update Call

Delete a specific call and its associated data

Delete Call

Create Phone Number

Retrieve details of a specific phone number

Get Phone Number

List Phone Numbers

Update agent bound to a purchased phone number

Update Phone Number

Delete Phone Number

Create Agent

Get Agent

List Agents

Update Agent

Delete Agent

Get Agent Versions

Create a new Retell LLM Response Engine that can be attached to an agent. This is used to generate response output for the agent.

Create Retell LLM

Retrieve details of a specific Retell LLM Response Engine

Get Retell LLM

List all Retell LLM Response Engines that can be attached to an agent.

List Retell LLMs

Update an existing Retell LLM Response Engine

Update Retell LLM

Delete an existing Retell LLM Response Engine

Delete Retell LLM

Create Knowledge Base

Retrieve details of a specific knowledge base

Get Knowledge Base

List Knowledge Bases

Delete Knowledge Base

Add Knowledge Base Sources

Delete an existing source from knowledge base

Delete Knowledge Base Source

Get Voice

List Voices

Create Batch Call

Get the current concurrency and concurrency limit of the org

Get Concurrency

Import a phone number from custom telephony & Bind agents

Import Phone Number

Register a new phone call for custom telephony

Register Phone Call

Retell AI connects with your server, and get responses / actions from your custom LLM.

LLM WebSocket

Explore Retell AI’s video hub—submit your YouTube features, request new tutorials, and follow us for the latest updates. 

Retell AI Video Hub - Introduction

For Beginners

By Features

By Use Cases

Spanish Video

German Videos

Deprecating on 5/30/2025

Community

Changelog

Status

Pricing

Enterprise Plan

API Reference

Video Tutorials

Deprecation Notice

Dashboard

Homepage

Support

Compliance

Conversation Flow Overview

Step 1: Configure global settings

Step 3: Add transition conditions

How to improve your conversation flow agent's performance

Debug guide

Step 2: Configure the basic settings

Guide on how to select the right transcription mode for your agent.

Balance between transcription accuracy and latency

Handle background speech & noise

General prompt engineering guide

Prompt guide & examples for specific situations

A step by step guide to setup different LLM options

Configure LLM options

Choose a custom voice

Add custom pronunciation

Normalize text for speech

Add backchannel

Make agent respond nothing

Add pause or read slowly

Guide to setup fallback voices for your agent.

Setup TTS fallback

Configure your AI agent to detect and handle voicemails automatically

Handle voicemail

Configure your AI agent to handle DTMF input from the user

Capture DTMF input from user

Knowledge Base

Learn how to personalize your agent's responses using dynamic variables

Dynamic Variables

Learn how to effectively test and debug your AI agents using the LLM Playground

Manually test your agent

Debug your agent response

Automatically test your agent

Batch test your agent

Web call testing

A step by step guide to integrate custom telephony providers

Custom Telephony Overview

A step by step guide to make phone calls with Retell managed numbers & imported numbers

Outbound calls (make calls)

A step-by-step guide to creating and managing batch calls.

Overview - Batch Calls

Create batch calls

Monitor batch calls

Call Efficiently Overview

Add a business profile

Apply for verified phone number

Apply for branded call

Handle application rejection

Stop the service

Secure the webhook

Post Call Analysis Overview

Define the information you want to extract

Consume the analysis data

Check estimated latency

Check actual latency

Follow these steps to resolve high end-to-end latency issues.

Troubleshoot high latency

Troubleshooting Transcript Accuracy

How to fix when your AI agent gives incorrect responses

Debug wrong response

Debug call transfer failure

Debug call disconnection

Understand outbound call disconnection reasons.

Debug outbound connection issues

Learn how to monitor your workspace's usage, manage your subscription, and update billing information.

Get Started

Build

Test

Deploy

Monitor

Reliability & Debugging

Accounts and Workspace

Advanced Topics

Network Ecosystem

Phone call testing