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TaylorChen

Multi-MCPs

by TaylorChen

make_call

Initiate phone calls using Twilio by specifying recipient, sender, and TwiML URL for call behavior.

Instructions

Make a phone call via Twilio with a TwiML URL

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
toYes
fromYes
twiml_urlYes

Implementation Reference

  • Handler function that executes the 'make_call' tool: validates inputs (to, from, twiml_url) and calls TwilioClient.makeCall.
    async make_call(args: Record<string, unknown>) {
      if (!cfg.twilioAccountSid || !cfg.twilioAuthToken) throw new Error("TWILIO_ACCOUNT_SID/TWILIO_AUTH_TOKEN are not configured");
      const to = String(args.to || "");
      const from = String(args.from || "");
      const twimlUrl = String(args.twiml_url || "");
      if (!to || !from || !twimlUrl) throw new Error("to, from, twiml_url are required");
      return client.makeCall(to, from, twimlUrl);
    },
  • Input schema definition for the 'make_call' tool specifying required string parameters: to, from, twiml_url.
    inputSchema: {
      type: "object",
      properties: { to: { type: "string" }, from: { type: "string" }, twiml_url: { type: "string" } },
      required: ["to", "from", "twiml_url"],
    },
  • Registration of the 'make_call' tool in the tools array returned by registerTwilio().
    {
      name: "make_call",
      description: "Make a phone call via Twilio with a TwiML URL",
      inputSchema: {
        type: "object",
        properties: { to: { type: "string" }, from: { type: "string" }, twiml_url: { type: "string" } },
        required: ["to", "from", "twiml_url"],
      },
    },
  • TwilioClient.makeCall helper method that sends POST request to Twilio API to initiate the call.
    makeCall(to: string, from: string, twimlUrl: string) {
      const form = new URLSearchParams({ To: to, From: from, Url: twimlUrl });
      return this.request(`/Accounts/${this.accountSid}/Calls.json`, {
        method: "POST",
        headers: { Authorization: `Basic ${this.authHeader}`, "content-type": "application/x-www-form-urlencoded" },
        body: form as any,
      });
    }
Behavior2/5

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

With no annotations provided, the description carries full burden for behavioral disclosure. While 'Make a phone call' implies a write/mutation operation, the description doesn't disclose any behavioral traits such as authentication requirements, rate limits, cost implications, error conditions, or what happens when the call completes. This leaves significant gaps for an agent to understand the tool's behavior.

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

Conciseness5/5

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

The description is extremely concise at just 8 words, front-loading the core purpose immediately. Every word earns its place by specifying the action, service provider, and key technical requirement. There's zero waste or redundancy in this minimal description.

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

Completeness2/5

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

For a mutation tool with 3 required parameters, 0% schema coverage, no annotations, and no output schema, the description is incomplete. It doesn't explain what the tool returns, what errors might occur, authentication requirements, or provide enough context for an agent to use it effectively. The extreme conciseness comes at the cost of necessary contextual information.

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

Parameters2/5

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

With 0% schema description coverage and 3 required parameters, the description provides no information about parameter meanings beyond what can be inferred from the parameter names ('to', 'from', 'twiml_url'). The description doesn't explain what format these parameters should be in, what a TwiML URL is, or any constraints on phone number formatting. This leaves the agent with insufficient guidance for proper parameter usage.

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

Purpose4/5

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

The description clearly states the action ('Make a phone call') and the resource/method ('via Twilio with a TwiML URL'), providing a specific verb+resource combination. However, it doesn't differentiate from the sibling tool 'send_sms' which also uses Twilio for communication, leaving some ambiguity about when to choose one over the other.

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

Usage Guidelines2/5

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

The description provides no guidance on when to use this tool versus alternatives. There's no mention of prerequisites, when-not-to-use scenarios, or comparison with the sibling 'send_sms' tool that also appears to be a Twilio communication method. The agent must infer usage context from the tool name alone.

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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