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end_call

The end_call tool lets agents hang up a phone call after saying goodbye. Instead of waiting indefinitely for the caller to disconnect, the agent can end the call programmatically via Twilio’s REST API.

When It’s Registered

This tool is always available — every agent has access to end_call regardless of configuration. The system injects usage instructions into the agent’s system prompt automatically.

Tool Definition

{
  "name": "end_call",
  "description": "Ends the current phone call. Use this tool after you have said your final goodbye and the conversation is complete. IMPORTANT: wait a moment after saying goodbye before calling this tool, so the caller hears your farewell before the call disconnects.",
  "parameters": {
    "type": "object",
    "properties": {},
    "required": []
  }
}

The tool takes no parameters — the agent simply invokes it when ready to hang up.

Execution Flow

Model calls end_call({})
  → Send mark event to Twilio after buffered farewell audio
  → Twilio plays all buffered audio, then echoes mark back
  → On mark echo: call Twilio REST API to end the call
  → Safety net: if mark echo never arrives, force hangup after 15 seconds

Twilio REST API Call

POST https://api.twilio.com/2010-04-01/Accounts/{AccountSid}/Calls/{CallSid}.json
Authorization: Basic {base64(AccountSid:AuthToken)}
Content-Type: application/x-www-form-urlencoded

Status=completed

Setting the call status to completed immediately terminates the call for both parties.

Usage Instructions

The system automatically injects instructions into every agent’s prompt:

“After saying goodbye and completing the conversation, use the end_call tool to hang up. Wait a moment after saying goodbye before calling this tool, so the caller hears your farewell before the call disconnects.”

Implementation Files

File	Purpose
`build_end_call_tool_definition_service.rs`	Returns the tool definition
`handle_end_call_tool_call_service.rs`	Calls Twilio REST API to set call status to `completed`
`collect_agent_tools_service.rs`	Registers `end_call` for all agents
`end_call_util.rs`	Twilio REST API helper

Error Handling

Missing Twilio credentials → AppError::InvalidInput
Twilio API request fails → AppError::Internal with error details

Agent Tools Overview — voice and task tool systems
Agent — agent session setup and tool collection