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Features

Advanced capabilities available in the Patter TypeScript SDK.

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Call Recording

Enable call recording via the Twilio Recordings API. Recordings are stored in your Twilio account. 
await phone.serve({
  agent,
  recording: true,
  onCallEnd: async (data) => {
    console.log("Recording available in your Twilio console");
  },
});
Recording is only available with Twilio. Telnyx recording is not yet supported.
The SDK sets up a /webhooks/twilio/recording endpoint to receive recording status callbacks. Recording URLs are logged to the console when they become available.

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Answering Machine Detection (AMD)

Detect voicemail systems on outbound calls and optionally leave a message. AMD is available with Twilio only. 
await phone.call({
  to: "+15559876543",
  agent,
  machineDetection: true,
  voicemailMessage: "Hi, this is Acme Corp calling about your appointment tomorrow. Please call us back at 555-000-1234.",
});
When AMD detects a machine (after the beep or after silence), the SDK automatically:
  1. Plays the voicemailMessage as TwiML
  2. Hangs up the call
If no voicemailMessage is set, the call proceeds normally even when a machine is detected.

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DTMF Input

Keypad presses (DTMF tones) during a call are automatically forwarded to the AI agent as text in the format [DTMF: N], where N is the digit pressed (0-9, *, #). 
User presses "1" → Agent receives: [DTMF: 1]
User presses "#" → Agent receives: [DTMF: #]
No additional configuration is needed. The AI agent’s system prompt can include instructions on how to handle DTMF input: 
const agent = phone.agent({
  systemPrompt: `You are an IVR system. When the user presses:
- 1: Transfer to sales
- 2: Transfer to support  
- 0: Transfer to operator
Respond to [DTMF: N] inputs accordingly.`,
});

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Call Transfer

The transfer_call system tool is automatically available to every agent. The AI model invokes it when the caller asks to speak to a human. 
const agent = phone.agent({
  systemPrompt: `You are a front desk assistant. If the caller wants to speak to a human, transfer them to +15559876543.`,
});
When the transfer tool is invoked, the SDK uses the Twilio REST API to redirect the active call to the target number.

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Barge-In

Patter supports barge-in — the caller can interrupt the AI agent while it is speaking. The SDK uses mark-based audio tracking to detect when the caller starts speaking during AI playback. When barge-in occurs:
  1. The current TTS audio is immediately stopped
  2. The caller’s speech is processed normally
  3. The AI generates a new response
No configuration is needed. Barge-in is always active.

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Dynamic Variables

Use {placeholder} syntax in system prompts for per-call customization: 
const agent = phone.agent({
  systemPrompt: "You are a support agent for {company}. The caller is {caller_name} with account {account_id}.",
  variables: {
    company: "Acme Corp",
    caller_name: "Default",
    account_id: "unknown",
  },
});

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Per-Call Variable Override

Override agent-level variables for individual outbound calls: 
await phone.call({
  to: "+15559876543",
  agent,
  variables: {
    caller_name: "Jane Smith",
    account_id: "ACC-12345",
  },
});
Call-level variables are merged with agent-level variables, with call-level taking precedence.
Variables are sanitized before substitution. Keys like __proto__, constructor, and prototype are stripped to prevent prototype pollution.

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Conversation History

Every call maintains a conversation history that accumulates throughout the call. The history is:
  • Passed to onMessage callbacks as data.history
  • Included in onCallEnd as data.transcript
  • Capped at 200 entries per call (oldest entries are dropped when the limit is reached)
Each entry contains: 
{
  role: string;       // "user" or "assistant"
  text: string;       // Transcript text
  timestamp: number;  // Unix timestamp (ms)
}

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AI Disclosure

An AI disclosure message is automatically played at the start of every call. This is non-optional and ensures compliance with regulations requiring callers to be informed they are speaking with an AI.

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Outbound Calls

Make outbound calls in local mode: 
// Twilio
await phone.call({
  to: "+15559876543",
  agent,
});

// With AMD and voicemail
await phone.call({
  to: "+15559876543",
  agent,
  machineDetection: true,
  voicemailMessage: "Please call us back.",
});

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LocalCallOptions

ParameterTypeRequiredDefaultDescription
tostringYes—Destination phone number (E.164 format).
agentAgentOptionsYes—Agent configuration for the call.
machineDetectionbooleanNofalseEnable AMD (Twilio only).
voicemailMessagestringNo—Message to leave on voicemail. Requires machineDetection: true.
variablesRecord<string, string>No—Per-call variable overrides merged into agent.variables.
The to parameter must be in E.164 format (e.g., +15559876543). The SDK validates this and throws if the format is invalid.