POST /create-agent

Changed on Oct 29, 2026

Create a new agent

Request

Base URL
https://api.retellai.com
Auth
HTTP bearer

Request body

agent_namestring nullable

The name of the agent. Only used for your own reference.

version_descriptionstring nullable

Optional description of the agent version. Used for your own reference and documentation.

version_titlestring nullable

Optional title of the agent version. Used for your own reference.

voice_idstring required

Unique voice id used for the agent. Find list of available voices and their preview in Dashboard.

Select the voice model used for the selected voice. Each provider has a set of available voice models. Set to null to remove voice model selection, and default ones will apply. Check out dashboard for more details of each voice model.

fallback_voice_idsstring[] nullable

When TTS provider for the selected voice is experiencing outages, we would use fallback voices listed here for the agent. Voice id and the fallback voice ids must be from different TTS providers. The system would go through the list in order, if the first one in the list is also having outage, it would use the next one. Set to null to remove voice fallback for the agent.

voice_temperaturenumber

Controls how stable the voice is. Value ranging from [0,2]. Lower value means more stable, and higher value means more variant speech generation. Check the dashboard to see what provider supports this feature. If unset, default value 1 will apply.

voice_speednumber

Controls speed of voice. Value ranging from [0.5,2]. Lower value means slower speech, while higher value means faster speech rate. If unset, default value 1 will apply.

enable_dynamic_voice_speedboolean

If set to true, will enable dynamic voice speed adjustment based on the user's speech rate and conversation context. If unset, default value false will apply.

enable_dynamic_responsivenessboolean

If set to true, the agent will dynamically adjust how quickly it responds based on the user's speech rate and past turn-taking behavior in the call. If unset, default value false will apply.

volumenumber

If set, will control the volume of the agent. Value ranging from [0,2]. Lower value means quieter agent speech, while higher value means louder agent speech. If unset, default value 1 will apply.

enable_expressive_modeboolean

Master toggle for expressive mode. When true, the agent may add expressive voice tags to the audio it generates. Only applicable for platform voices. If unset, defaults to false.

expressive_emotion_tagsstring[]

The expressive voice tags Retell pre-teaches the model to use when enable_expressive_mode is true. Custom tags defined in the system prompt are still allowed. If empty, the agent follows general expressive guidance without a fixed tag set.

expressive_mode_promptstring nullable

Custom expressive voice guidance to use instead of the default Retell expressive prompt when enable_expressive_mode is true. If omitted or blank, the default expressive prompt will be used.

responsivenessnumber

Controls how responsive is the agent. Value ranging from [0,1]. Lower value means less responsive agent (wait more, respond slower), while higher value means faster exchanges (respond when it can). If unset, default value 1 will apply.

interruption_sensitivitynumber

Controls how sensitive the agent is to user interruptions. Value ranging from [0,1]. Lower value means it will take longer / more words for user to interrupt agent, while higher value means it's easier for user to interrupt agent. If unset, default value 1 will apply. When this is set to 0, agent would never be interrupted.

enable_backchannelboolean

Controls whether the agent would backchannel (agent interjects the speaker with phrases like "yeah", "uh-huh" to signify interest and engagement). Backchannel when enabled tends to show up more in longer user utterances. If not set, agent will not backchannel.

backchannel_frequencynumber

Only applicable when enable_backchannel is true. Controls how often the agent would backchannel when a backchannel is possible. Value ranging from [0,1]. Lower value means less frequent backchannel, while higher value means more frequent backchannel. If unset, default value 0.8 will apply.

backchannel_wordsstring[] nullable

Only applicable when enable_backchannel is true. A list of words that the agent would use as backchannel. If not set, default backchannel words will apply. Check out backchannel default words for more details. Note that certain voices do not work too well with certain words, so it's recommended to experiment before adding any words.

reminder_trigger_msnumber

If set (in milliseconds), will trigger a reminder to the agent to speak if the user has been silent for the specified duration after some agent speech. Must be a positive number. If unset, default value of 10000 ms (10 s) will apply.

reminder_max_countinteger

If set, controls how many times agent would remind user when user is unresponsive. Must be a non negative integer. If unset, default value of 1 will apply (remind once). Set to 0 to disable agent from reminding.

If set, will add ambient environment sound to the call to make experience more realistic. Currently supports the following options:

coffee-shop: Coffee shop ambience with people chatting in background. Listen to Ambience
convention-hall: Convention hall ambience, with some echo and people chatting in background. Listen to Ambience
summer-outdoor: Summer outdoor ambience with cicada chirping. Listen to Ambience
mountain-outdoor: Mountain outdoor ambience with birds singing. Listen to Ambience
static-noise: Constant static noise. Listen to Ambience
call-center: Call center work noise. Listen to Ambience Set to null to remove ambient sound from this agent.

ambient_sound_volumenumber

If set, will control the volume of the ambient sound. Value ranging from [0,2]. Lower value means quieter ambient sound, while higher value means louder ambient sound. If unset, default value 1 will apply.

webhook_urlstring nullable

The webhook for agent to listen to call events. See what events it would get at webhook doc. If set, will binds webhook events for this agent to the specified url, and will ignore the account level webhook for this agent. Set to null to remove webhook url from this agent.

webhook_eventsstring[] nullable

Which webhook events this agent should receive. If not set, defaults to call_started, call_ended, call_analyzed.

webhook_timeout_msinteger

The timeout for the webhook in milliseconds. If not set, default value of 10000 will apply.

boosted_keywordsstring[] nullable

Provide a customized list of keywords to bias the transcriber model, so that these words are more likely to get transcribed. Commonly used for names, brands, street, etc. Entries may reference dynamic variables with {{variable}} syntax.

data_storage_setting'everything' | 'everything_except_pii' | 'basic_attributes_only'

Granular setting to manage how Retell stores sensitive data (transcripts, recordings, logs, etc.). This replaces the deprecated opt_out_sensitive_data_storage field.

everything: Store all data including transcripts, recordings, and logs.
everything_except_pii: Store data without PII when PII is detected.
basic_attributes_only: Store only basic attributes; no transcripts/recordings/logs. If not set, default value of "everything" will apply.

data_storage_retention_daysinteger nullable

Number of days to retain call/chat data before automatic deletion. Must be between 1 and 730 days. If not set, data is retained forever (no automatic deletion).

opt_in_signed_urlboolean

Whether this agent opts in for signed URLs for public logs and recordings. When enabled, the generated URLs will include security signatures that restrict access and automatically expire after 24 hours.

signed_url_expiration_msinteger nullable

The expiration time for the signed url in milliseconds. Only applicable when opt_in_signed_url is true. If not set, default value of 86400000 (24 hours) will apply.

enable_dnc_detectionboolean

If set to true, the agent recognizes requests to stop calling or contacting the user, confirms once, and on a clear yes ends the call with disconnection reason user_requested_dnc and sets do_not_call to true on the contact for the user's phone number. If unset, default value false will apply.

end_call_after_silence_msinteger

If users stay silent for a period after agent speech, end the call. The minimum value allowed is 10,000 ms (10 s). By default, this is set to 600000 (10 min).

max_call_duration_msinteger

Maximum allowed length for the call, will force end the call if reached. The minimum value allowed is 60,000 ms (1 min), and maximum value allowed is 7,200,000 (2 hours). By default, this is set to 3,600,000 (1 hour).

Available LLM models for agents.

begin_message_delay_msinteger

If set, will delay the first message by the specified amount of milliseconds, so that it gives user more time to prepare to take the call. Valid range is [0, 5000]. If not set or set to 0, agent will speak immediately. Only applicable when agent speaks first.

ring_duration_msinteger

If set, the phone ringing will last for the specified amount of milliseconds. This applies for both outbound call ringtime, and call transfer ringtime. Default to 30000 (30 s). Valid range is [5000, 300000].

stt_mode'fast' | 'accurate' | 'custom'

If set, determines whether speech to text should focus on latency or accuracy. Default to fast mode. When set to custom, custom_stt_config must be provided.

vocab_specialization'general' | 'medical'

If set, determines the vocabulary set to use for transcription. This setting only applies for English agents, for non English agent, this setting is a no-op. Default to general.

allow_user_dtmfboolean

If set to true, DTMF input will be accepted and processed. If false, any DTMF input will be ignored. Default to true.

allow_dtmf_interruptionboolean

If set to true, DTMF input will interrupt the agent even when interruption_sensitivity is 0. Can be overridden per conversation or subagent node. Default to false.

denoising_mode'no-denoise' | 'noise-cancellation' | 'noise-and-background-speech-cancellation'

If set, determines what denoising mode to use. Use "no-denoise" to bypass all audio denoising. Default to noise-cancellation.

denoising_enhancement_levelnumber nullable

Controls the enhancement level for background voice cancellation. Set to 0 to bypass background voice cancellation without BVC charges. Value ranging from [0,1]. Only applicable when denoising_mode is noise-and-background-speech-cancellation. Defaults to 0.8 if no value is configured. Set to null to clear the configured value. Omitting this field preserves the existing value.

timezonestring nullable

IANA timezone for the agent (e.g. America/New_York). Defaults to America/Los_Angeles if not set.

is_transfer_agentboolean

Whether to create the agent as a transfer agent for agentic warm transfer. You can only set this field when creating the agent. The response engine must also be configured for transfer use with is_transfer_llm or is_transfer_cf. Custom LLM agents cannot be transfer agents.

Example request

{
  "agent_name": "Jarvis",
  "version_description": "Customer support agent for handling product inquiries",
  "version_title": "Production hotfix",
  "voice_id": "retell-Cimo",
  "fallback_voice_ids": [
    "cartesia-Cimo",
    "minimax-Cimo"
  ],
  "voice_temperature": 1,
  "voice_speed": 1,
  "enable_dynamic_voice_speed": true,
  "enable_dynamic_responsiveness": true,
  "volume": 1,
  "enable_expressive_mode": true,
  "expressive_emotion_tags": [
    "empathetic",
    "excited",
    "sigh",
    "clear throat",
    "emphasis"
  ],
  "expressive_mode_prompt": "Use [sigh] for thoughtful pauses and [excited] for good news.",
  "responsiveness": 1,
  "interruption_sensitivity": 1,
  "enable_backchannel": true,
  "backchannel_frequency": 0.9,
  "backchannel_words": [
    "yeah",
    "uh-huh"
  ],
  "reminder_trigger_ms": 10000,
  "reminder_max_count": 2,
  "ambient_sound_volume": 1,
  "language": "en-US",
  "webhook_url": "https://webhook-url-here",
  "webhook_timeout_ms": 10000,
  "boosted_keywords": [
    "retell",
    "kroger"
  ],
  "data_storage_setting": "everything",
  "data_storage_retention_days": 30,
  "opt_in_signed_url": true,
  "signed_url_expiration_ms": 86400000,
  "pronunciation_dictionary": [
    {
      "word": "actually",
      "alphabet": "ipa",
      "phoneme": "ˈæktʃuəli"
    }
  ],
  "end_call_after_silence_ms": 600000,
  "max_call_duration_ms": 3600000,
  "voicemail_option": {
    "action": {
      "type": "static_text",
      "text": "Please give us a callback tomorrow at 10am."
    }
  },
  "ivr_option": {
    "action": {
      "type": "hangup"
    }
  },
  "call_screening_option": {
    "agent_identity": "Acme Health scheduling team",
    "call_purpose": "confirming your appointment for tomorrow"
  },
  "post_call_analysis_data": [
    {
      "type": "string",
      "name": "customer_name",
      "description": "The name of the customer.",
      "examples": [
        "John Doe",
        "Jane Smith"
      ]
    }
  ],
  "begin_message_delay_ms": 1000,
  "ring_duration_ms": 30000,
  "stt_mode": "fast",
  "vocab_specialization": "general",
  "allow_user_dtmf": true,
  "user_dtmf_options": {
    "termination_key": "#"
  },
  "denoising_mode": "noise-cancellation",
  "denoising_enhancement_level": 0.8,
  "timezone": "America/New_York",
  "pre_session_tools": [
    {
      "response_variables": {
        "contact_first_name": "data.first_name"
      },
      "output_selection": {
        "fields": [
          "id",
          "properties.email"
        ]
      }
    }
  ],
  "post_session_tools": [
    {
      "response_variables": {
        "contact_first_name": "data.first_name"
      },
      "output_selection": {
        "fields": [
          "id",
          "properties.email"
        ]
      }
    }
  ]
}

Response

Successfully created a new agent.

agent_idstring required

Unique id of agent.

versioninteger required

Version of the agent.

base_versioninteger nullable

Version that this draft was based on. Null for initial versions.

assigned_tagsstring[]

Tags assigned to this agent version. Preferred tag is listed first.

is_publishedboolean

Whether the agent is published.