Array of built-in tools. Each tool has a type field and tool-specific fields. On Update Assistant, this replaces all existing built-in tools — pass an empty array [] to remove all tools.
Show Tool Types
call_transfer - Transfer the call to another phone number
phone_number (required): Phone number to transfer to
description: When to transfer the call
custom: If true, AI can determine transfer number dynamically
timezone: Timezone for transfer availability
warm_transfer: Send a message to the customer before transferring (default: false)
warm_transfer_message: Prompt telling the AI what to say before transferring (e.g., “Tell the customer that the call is being transferred.”)
warm_call_transfer - Warm transfer with supervisor briefing
supervisor_phone (required): Phone number to dial for the warm transfer (e.g., “+14155552001”). If custom_sip is enabled, this is a SIP address or internal extension instead.
outbound_phone_id (required): ID of the phone number used to dial the supervisor. See Retrieve Phone Numbers.
description (required): When to transfer — describes when the AI should initiate the warm transfer (e.g., “Transfer the call to a human supervisor when the customer requests to speak with a real person.”)
custom_sip: Enable to enter a custom SIP address or internal extension instead of a phone number (default: false)
caller_id_mode: What phone number the supervisor sees when receiving the call. Options: outbound_number (default — shows the outbound phone number), customer_number (shows the caller’s number), custom (shows a custom number)
custom_caller_id: Custom phone number shown to supervisor. Only used when caller_id_mode is custom.
hold_music: Audio played to the caller while on hold. Options: hold_music (default — plays default hold music), none (silence, no music)
hold_music_volume: Volume level for hold music, 0–100 (default: 80)
hold_message: Message spoken to caller before placing them on hold (default: “Please hold while I connect you with a supervisor.”)
summary_instructions: Instructions for how the AI should brief the supervisor about the call (default: “Introduce the conversation from your perspective:\n- WHO is calling (name, company if mentioned)\n- WHY they called (their goal or problem)\n- WHY a human is needed at this point\n\nKeep it brief (2-3 sentences).”)
briefing_initial_message: The first message the AI says to the supervisor when they answer (default: “Hello! I have a caller on the line who needs your assistance. May I brief you on the situation?”)
connected_message: Message spoken to caller after supervisor is connected (default: “You are now connected with a supervisor. I’ll leave you to it.”)
end_call - End the call programmatically
description: When the AI should end the call
dtmf_input - Send DTMF tones (keypad input)
description: When to use DTMF input (for IVR navigation)
collect_keypad - Collect keypad input from the caller
timeout: Seconds to wait for input, 1–30 (default: 5)
stop_key: Key that ends input. Options: # (default), *
calendar_integration - Schedule appointments via Cal.com
calcom_api_key (required): Your Cal.com API key
calcom_event_slug (required): The event type slug from Cal.com
calcom_team_slug: Team slug if the event belongs to a Cal.com team
calcom_endpoint: Cal.com API region. Options: us (default — https://api.cal.com), eu (https://api.cal.eu), custom (uses calcom_custom_endpoint)
calcom_custom_endpoint: Custom Cal.com API base URL. Only used when calcom_endpoint is custom (e.g., https://my-calcom-instance.com).
calcom_booking_fields: Array of custom booking fields for the event. Each field has: slug (required), type (required, e.g. “text”, “email”, “phone”, “select”), label (required), required (default: false), options (array of options for select fields)
description: When to offer scheduling
assistant_transfer - Hand off the conversation to a different AI assistant mid-call (swaps voice, LLM, and STT to the target assistant)
assistant_id (required): ID of the target assistant. Must belong to your account and cannot be the assistant being updated (no self-transfer).
description: When to transfer (max 500 chars, default: “Transfer the conversation to this assistant when appropriate.”)
message_before_transfer: Optional message the AI speaks before switching to the target assistant (max 500 chars).
speak_transfer_greeting: If true, the target assistant speaks its configured initial message after the transfer completes (default: true)
"tools": [ { "type": "dtmf_input", "description": "Navigate IVR when needed" }, { "type": "warm_call_transfer", "supervisor_phone": "+1234567890", "outbound_phone_id": 7, "description": "Transfer the call to a human supervisor when the customer requests to speak with a real person.", "custom_sip": false, "caller_id_mode": "outbound_number", "hold_music": "hold_music", "hold_music_volume": 80, "hold_message": "Please hold while I connect you with a supervisor.", "summary_instructions": "Introduce the conversation from your perspective:\n- WHO is calling (name, company if mentioned)\n- WHY they called (their goal or problem)\n- WHY a human is needed at this point\n\nKeep it brief (2-3 sentences).", "briefing_initial_message": "Hello! I have a caller on the line who needs your assistance. May I brief you on the situation?", "connected_message": "You are now connected with a supervisor. I'll leave you to it." }, { "type": "collect_keypad", "timeout": 5, "stop_key": "#" }, { "type": "assistant_transfer", "assistant_id": 14765, "description": "Transfer to the Support Assistant when the customer needs technical help.", "message_before_transfer": "Sure — let me transfer you to our support specialist.", "speak_transfer_greeting": true }, { "type": "end_call", "description": "End call when done" }]
When you list assistants, each configured tool is returned as { "type": "...", "data": { ... } } with the same field names nested under data (not top-level).
{ "name": "Sales Assistant", "voice_id": 1, "language_id": 1, "type": "outbound", "mode": "pipeline", "timezone": "Europe/Berlin", "initial_message": "Hello! How can I assist you today?", "system_prompt": "You are a professional sales assistant...", "llm_model_id": 2, "secondary_language_ids": [2, 3], "knowledgebase_id": 1, "knowledgebase_mode": "prompt", "fillers": true, "filler_config": { "positive": ["Great!", "Perfect!", "Very good!"], "negative": ["Hmm.", "Understood."], "question": ["Good question.", "One moment."], "neutral": ["Okay.", "Noted.", "Understood."] }, "tool_ids": [1, 5], "tools": [ {"type": "dtmf_input", "description": "Navigate IVR when needed"}, { "type": "warm_call_transfer", "supervisor_phone": "+1234567891", "outbound_phone_id": 7, "description": "Transfer the call to a human supervisor when the customer requests to speak with a real person.", "custom_sip": false, "caller_id_mode": "outbound_number", "hold_music": "hold_music", "hold_music_volume": 80, "hold_message": "Please hold while I connect you with a supervisor.", "summary_instructions": "Introduce the conversation from your perspective:\n- WHO is calling (name, company if mentioned)\n- WHY they called (their goal or problem)\n- WHY a human is needed at this point\n\nKeep it brief (2-3 sentences).", "briefing_initial_message": "Hello! I have a caller on the line who needs your assistance. May I brief you on the situation?", "connected_message": "You are now connected with a supervisor. I'll leave you to it." }, {"type": "collect_keypad", "timeout": 5, "stop_key": "#"}, { "type": "assistant_transfer", "assistant_id": 14765, "description": "Transfer to the Support Assistant when the customer needs technical help.", "message_before_transfer": "Sure — let me transfer you to our support specialist.", "speak_transfer_greeting": true }, {"type": "end_call", "description": "End call when the customer is satisfied"} ], "reengagement_interval": 20, "reengagement_prompt": "Are you still there?"}
