44 voice features that give your agent superpowers during live calls — call control, authentication, payments, analytics, compliance, and more.

Voice Tools & Features

Voice tools extend your agent's abilities during a live phone call. Unlike general tools (Google Calendar, Sheets, etc.), voice tools interact directly with the call itself — ending it, transferring it, sending an SMS mid-conversation, collecting payments, or authenticating callers.

thinnestAI provides 44 voice features organized into categories below. Some features expose callable tools to the LLM (the agent decides when to use them), while others inject behavior via the system prompt or run automatically.

Call Control

Core tools for managing the call lifecycle.

Tool	What It Does	LLM Tool
End Call	Programmatically end a call with configurable farewell messages	`end_call`
Transfer Call	Hand off to a human agent, department, or another AI agent	`transfer_to_{agent}`
Hold / Resume	Put the caller on hold while looking up information	`put_caller_on_hold`, `resume_from_hold`
Conference Calling	Add a third party (supervisor, specialist) to the call	`start_conference`
DTMF Input	Send or receive dial-tone keypresses during a call	via config
Voicemail Drop	Leave a pre-recorded message when voicemail is detected	`detected_answering_machine`

Communication

Send messages and visual content to the caller during or after the call.

Tool	What It Does	LLM Tool
SMS Mid-Call	Send a text message to the caller during a live call	`send_sms`
Visual IVR	Send a link to the caller's phone for forms, maps, or complex info	`send_visual_link`
Post-Call Follow-Up	Trigger emails, SMS, or webhooks after the call ends	automatic

Authentication & Security

Verify caller identity and enforce compliance.

Tool	What It Does	LLM Tool
Caller Authentication	Verify identity via PIN, DOB, passphrase, or custom credential	`verify_caller_identity`, `fail_caller_auth`
Voice Biometrics	Verify caller identity using voiceprint analysis	`verify_voice_identity`
Voice Approvals (HITL)	Get verbal confirmation before high-stakes actions	`request_voice_approval`, `record_approval_decision`
Compliance & Consent	Recording consent, guardrails, hallucination prevention	via config
Do-Not-Call List	Check numbers against DNC lists before outbound calls	`check_dnc_list`

Business Actions

Tools that perform real-world actions during the call.

Tool	What It Does	LLM Tool
Appointment Booking	Check availability and book calendar appointments	`check_availability`, `book_appointment`
Payment Processing	Collect PCI-compliant payments via Stripe or custom provider	`collect_payment`
MCP Server Integration	Call external tools via Model Context Protocol	`mcp_call`

Recording & Monitoring

Record, monitor, and analyze calls in real time.

Tool	What It Does	LLM Tool
Call Recording	Record calls with consent management	via config
Call Queue	Queue callers when all agents are busy	via config
Live Call Monitoring	Supervisors can listen to or join active calls	via config

Analytics & Post-Call

Track performance, detect gaps, and sync with external systems.

Tool	What It Does	LLM Tool
Conversion Tracking	Record conversion events when goals are met	`track_conversion`
Post-Call Survey	Ask a survey question before ending the call	`record_survey_response`
Sentiment Escalation	Detect negative sentiment and escalate to a human	`escalate_sentiment`
Analytics & Monitoring	Call scoring, CRM sync, knowledge gap detection, speed-to-lead	automatic

Voice & Language

Control how the agent sounds and handles multiple languages.

Tool	What It Does	LLM Tool
Multilingual Auto-Switch	Detect language and switch TTS/STT mid-call	`switch_language`
Call Experience Features	Pace control, silence fillers, backchanneling, greeting variants, and more	via config

Adding Voice Tools to Your Agent

Voice tools are configured in the Voice Settings section of your agent, separate from general tools.

Via the Dashboard

Open your agent in the dashboard.
Scroll to the Voice Settings section.
Enable the tools you need (e.g., toggle End Call, Transfer, DTMF).
Configure each tool's settings (e.g., transfer destination number, SMS template).
Click Save.

Via the API

{
  "voiceEnabled": true,
  "endCallEnabled": true,
  "interruptionConfig": { "enabled": true, "threshold": 0.5 },
  "recordingConfig": { "enabled": true },
  "silenceConfig": {
    "unresponsiveTimeoutSeconds": 30,
    "fillersEnabled": true,
    "fillerPhrases": ["Let me check that for you...", "One moment please..."]
  },
  "webhookConfig": {
    "url": "https://your-server.com/webhook",
    "events": ["call_started", "call_ended"]
  }
}

See the Create Agent API for the full voice configuration reference.

How Voice Tools Work

During a live call, your AI agent decides when to use a voice tool based on conversation context and your instructions. For example:

The caller asks to speak to a manager -> agent triggers Transfer Call
The caller says "goodbye" -> agent triggers End Call
The caller asks for a confirmation link -> agent triggers SMS Mid-Call
Voicemail detected on outbound call -> agent triggers Voicemail Drop
Caller's sentiment drops significantly -> agent triggers Sentiment Escalation
Caller wants to make a payment -> agent triggers Payment Processing

General vs. Voice Tools

	General Tools	Voice Tools
Scope	Any agent (chat, voice, workflow)	Voice agents only
Examples	Google Calendar, Gmail, Sheets, CRM	End Call, Transfer, DTMF, SMS, Payments
Configured in	Tools tab	Voice Settings
Trigger	Agent decides based on context	Agent decides + call events

Your agent can use both general tools and voice tools simultaneously. For example, during a call the agent might look up a calendar slot (general tool) and then send an SMS confirmation (voice tool).

Voice Tools Overview