@aiwerk/mcp-server-elevenlabs

register_twilio_call

Registers a Twilio call with agent and number details, returning TwiML to connect inbound or outbound calls.

Instructions

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "agent_id": "<agent_id>",
      "from_number": "<from_number>",
      "to_number": "<to_number>"
    },
    "name": "register_twilio_call"
  }
}

Input Schema

Name	Required	Description	Default
`agent_id`	Yes
`direction`	No
`to_number`	Yes
`from_number`	Yes
`conversation_initiation_client_data`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Sep 13, 2026

TDQS

C2.2/5.0

Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=false, destructiveHint=false, idempotentHint=false and openWorldHint=true, so the mutation/non-idempotent profile is covered. The description adds one genuine piece of context by noting it returns TwiML (useful since there is no output schema), but omits registration side effects, auth requirements, and error behavior.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

A single short sentence with no filler, so it is appropriately sized. It is under-specified rather than verbose, but the one sentence does carry the only two facts offered (registration and TwiML return).

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness1/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 5-parameter tool with 0% schema description coverage, a nested client-data object, no output schema, and many competing call-handling siblings, this one line is far too thin to let an agent invoke it correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters1/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0% across 5 parameters, including a complex nested conversation_initiation_client_data object, and the description supplies no parameter meaning at all. Nothing explains agent_id, direction, from_number, or to_number beyond their names.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose3/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (Register) and resource (Twilio Call) and adds the notable side effect of returning TwiML. However, it does nothing to distinguish this from close siblings such as handle_twilio_outbound_call or handle_exotel_outbound_call, so an agent cannot tell which to pick from the text alone.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines1/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives no indication of when to use this tool versus the many sibling call-handling tools (handle_twilio_outbound_call, handle_sip_trunk_outbound_call, whatsapp_outbound_call). There are no prerequisites, triggers, or exclusions stated.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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