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vapi-mcp

vapi-mcp

by BlaineHeffron
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

Place Vapi smoke-test call

smoke_test_call
Destructive

Initiate a billable outbound call to a customer number and retrieve the resulting transcript and structured data. Requires explicit confirmation before dialing.

Instructions

Place a real, potentially billable outbound call using the client assistant. Requires explicit confirmation. Optionally poll and return transcript and structured data.

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": {
      "clientSlug": "<clientSlug>",
      "customerNumber": "<customerNumber>",
      "confirmBillableCall": "<confirmBillableCall>"
    },
    "name": "smoke_test_call"
  }
}

Input Schema

NameRequiredDescriptionDefault
clientSlugYesStable local client slug: lowercase letters, digits, and internal hyphens
waitSecondsNo
phoneNumberIdNo
customerNumberYesE.164 phone number, for example +12125550123
confirmBillableCallYesMust be true because this places a real external call

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4/5.0
Behavior4/5

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

The description goes beyond annotations by disclosing that the call is real, potentially billable, and requires explicit confirmation, which complements the destructiveHint. It also mentions optional polling and returns, adding behavioral context not covered by structured fields.

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 two short sentences with the core action and key constraints front-loaded. It contains no fluff or repetition and is entirely on-topic.

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

Completeness4/5

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

For a tool that places a call, the description covers the essential points: billable, confirmation needed, and optional return of transcript/data. It doesn't clarify parameter interactions or output format, but the schema and annotations fill some gaps. Given no output schema, the mention of return data is helpful.

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

Parameters3/5

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

Schema description coverage is 60% (3/5 parameters have descriptions). The description does not add parameter-specific information beyond what's already in the schema; it only indirectly references confirmation. The undocumented parameters (waitSeconds, phoneNumberId) are not explained in the description.

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

Purpose5/5

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

The description clearly states the action (place an outbound call) and the resource (client assistant), and distinguishes it from sibling provisioning/config tools. It also adds critical context (billable, confirmation required) that sets it apart.

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

Usage Guidelines3/5

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

The description implies a smoke-testing use case from the title but gives no explicit guidance on when to use this tool versus alternatives. It does not mention when not to use it or name any sibling tools.

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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