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vapi-mcp

vapi-mcp

by BlaineHeffron
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

Attach inbound Vapi phone

attach_phone
Destructive

Bind an existing Vapi phone number or create/import one using provider-specific configuration, enforcing the client assistant association.

Instructions

Bind an existing Vapi phone-number ID, or create/import a number from a provider-specific Vapi REST body. The client assistantId is always enforced.

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>"
    },
    "name": "attach_phone"
  }
}

Input Schema

NameRequiredDescriptionDefault
clientSlugYesStable local client slug: lowercase letters, digits, and internal hyphens
phoneNumberIdNo
phoneConfigurationNoProvider-specific POST /phone-number body. Prefer a stored credentialId over embedding telephony credentials.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4.2/5.0
Behavior4/5

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

The description adds behavioral detail beyond annotations, such as the enforced 'client assistantId' and the ability to either bind an existing ID or create a new one. This provides insight into side effects, though it does not detail conflict handling or error cases.

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 a single, concise sentence that front-loads the primary action (bind or create/import) and avoids unnecessary detail. It is well-structured and efficient.

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?

Given the schema (with property descriptions) and annotations (destructive, non-idempotent), the description provides sufficient operational context. There is no output schema, so return values need not be explained. Minor gaps exist, such as behavior when both parameters are provided, but these are not critical.

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

Parameters4/5

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

The description clarifies the roles of phoneNumberId (existing ID to bind) and phoneConfiguration (body for creation/import), adding meaningful semantics beyond the schema's generic descriptions. It explains how the parameters relate to the two operational modes.

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 tool's purpose: to bind an existing Vapi phone-number ID or create/import a number via a provider-specific body. It distinguishes from sibling tools like attach_tools, which likely handle tools rather than phone numbers, making its role unambiguous.

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 usage by describing two modes (bind existing or create/import) but does not explicitly compare with alternatives like attach_tools or provision_client. It gives conditional guidance but lacks clear 'when to use this vs. that' instructions.

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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