Set up a Retell single or multi-prompt agent: choose the language model, pick a voice and speaking speed, and decide who speaks first on the call.
Three settings decide how your agent sounds and behaves before you write a word of prompt: the language model, the voice, and who speaks first. Set those, and the agent can hold a call.
1
Select a language model
Open the model dropdown in the agent toolbar. Models are grouped into Versatile and highly intelligent, Fast and cost-efficient, and Speech to speech, with the per-minute price next to each one.Start with any model marked Suggested. Those are the models we currently recommend for a good balance of response quality, latency, and cost, and the list is kept up to date as new models ship. You can switch models later without rewriting your prompt.
The model dropdown, with the Suggested pill on the first recommended model highlighted.
2
Choose a voice
Open the voice control in the agent toolbar, next to the model dropdown.
The voice control in the agent toolbar.
This opens the Select Voice dialog. Each voice card shows its accent, age, and provider, plus the voice ID you use when creating agents through the API — note the ID of the voice you pick. Press the play button on a card to hear a sample, and narrow the list with the Gender, Accent, and Search filters.
The Select Voice dialog. Each card carries a preview button and the voice ID.
Custom voices: to clone a voice, use Add voice clone on the Platform Voices tab. To bring a voice from your own provider account, switch to the Custom Providers tab and use Add custom voice. See the custom voice guide for both.Voice speed: the voice settings popover has a Voice Speed slider from 0.5x to 2.0x, defaulting to 1.0x. Check Dynamically adjust based on user input and the agent adapts its speaking speed to the user’s pace during the call: it tracks the user’s words per minute and gradually shifts its own speed to match. With this on, the user can also ask the agent to speak faster or slower mid-call. The checkbox isn’t available on speech-to-speech models, which control their own pacing.
3
Decide who speaks first
The Welcome Message setting below the prompt controls how a conversation opens:
User speaks first: the agent stays silent until the caller says something.
AI speaks first: the agent opens the conversation. A second dropdown then chooses how:
Dynamic message: the agent generates its own opener each call, based on your prompt.
Custom message: the agent reads a fixed message you type in the field below.
When the agent speaks first, Pause Before Speaking appears beside the setting. Raise it if the agent tends to start talking before the caller has finished picking up.
The Welcome Message setting with the second dropdown open on Dynamic message.
The panels on the right of the agent editor cover everything else. None are required to make a first call.
1
Write the prompt
The large box in the middle is where you specify the agent’s persona, identity, task, and guardrails. On a multi-prompt agent this text is the global prompt: it applies in every state and influences all response generation. See write a single prompt and write a multi prompt.
2
Configure Knowledge Base
Supply context to the agent as documents, URLs, or plain text. Read more at the knowledge base guide.
3
Configure Speech Settings
Fine-tune how the agent speaks and when it takes its turn.
Background sound: select a background sound that plays throughout the whole call to mimic an environment like a call center, making the conversation more humanlike and engaging.
Responsiveness: how responsive the agent is. Set it lower if you want the agent to wait longer before responding, which can be useful when talking to folks like the elderly. The lower the value, the more wait time is added before the agent responds. You can also check “Dynamically adjust based on user input” to let the agent automatically tune its response timing during the call. When enabled, the agent observes how quickly the user speaks and adjusts accordingly — slower speakers get more patient response timing, while faster speakers get quicker responses.
Interruption Sensitivity: how fast the agent gets interrupted by user interruptions. Set it lower if you want the agent to be more resilient to background speech.
Backchanneling: Set up how often and what words the agent uses to acknowledge users.
Boosted Keywords: Provides some biases towards certain words, making it easier to get recognized. Common ones are brand names, people’s names, etc.
Speech Normalization: convert entities like date, currency, numbers into plain words, which can help prevent issues where audio generated was not pronouncing those right.
Reminder frequency: how often the agent will remind the user when user is inactive.
Here are a couple of settings that are more call operation related.
Voicemail related settings: set up voicemail detection and what to do when voicemail is detected. See more at Handle Voicemail.
End call on silence: set up if user is inactive for a certain amount of time, the call will be ended.
Call duration: set up maximum duration of the call.
Pause before speaking: For the beginning of the call, if agent speaks first, it will wait for the configured duration before speaking, useful to handle scenarios when user is still picking up the phone.
5
Configure Realtime Transcription Settings
Tune how the agent hears the caller.
Denoising Mode: how aggressively background noise is filtered out of the caller’s audio.
Transcription Mode: which speech-to-text model transcribes the call.
Endpointing: how long the agent waits before deciding the caller has finished a turn.
Vocabulary Specialization: bias transcription toward a domain’s terms, so words like drug or product names come through correctly.
6
Configure Post-Call Data Extraction
Pull structured results out of each finished call, such as whether the appointment was booked or what the caller asked for. Usually worth setting up later, once the agent handles calls well. Read more at the post-call analysis guide.
7
Configure Security & Fallback Settings
Data Storage and PII Settings: opt out of storing recordings, transcripts, or personally identifiable information.
Secure URLs: serve recordings and logs from signed links that expire, anywhere from 1 minute to 7 days.
Fallback Voice: the voice to switch to if your primary voice provider fails mid-call, so the call continues instead of dropping.
Guardrails: limits on what the agent is allowed to say.
Default Dynamic Variables: fallback values for prompt variables that aren’t supplied when the call starts.
8
Configure Webhook Settings
Point the agent at your endpoint to receive call events. See register a webhook.
9
Configure MCPs
Connect the agent to external tools through a Model Context Protocol server. See MCP.
