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vapi-mcp

vapi-mcp

by BlaineHeffron
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

Attach Vapi tools

attach_tools
Destructive

Attach or create reusable Vapi tools while preserving assistant model configuration. Supports transfer, callback, calendar, CRM, API-request, and MCP tool payloads.

Instructions

Create reusable Vapi tools and/or attach existing tool IDs, preserving current assistant model configuration. Supports transfer, callback, calendar, CRM, API-request, and MCP tool payloads accepted by Vapi.

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_tools"
  }
}

Input Schema

NameRequiredDescriptionDefault
replaceNoReplace all attached tool IDs instead of merging them
clientSlugYesStable local client slug: lowercase letters, digits, and internal hyphens
existingToolIdsNo
toolDefinitionsNo

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A3.9/5.0
Behavior3/5

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

Annotations already flag destructive behavior and non-idempotency. The description adds useful context by noting that model configuration is preserved and listing supported tool payload types. It does not explain destructive replace semantics, but the annotations carry much of the safety burden.

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 sentences with no fluff. The purpose is front-loaded, and the second sentence provides practical scope without unnecessary detail.

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

Completeness3/5

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

For a tool that can replace or merge attached tool IDs and create arbitrary tool definitions, there is no mention of return values or the destructive implications of the replace flag. The description is adequate at a high level but leaves meaningful operational gaps for the agent.

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?

Schema description coverage is only 50%, so the description adds meaning by clarifying that existingToolIds attaches existing IDs and toolDefinitions accepts transfer, callback, calendar, CRM, API-request, and MCP payloads. This helps compensate for the sparse schema descriptions.

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: 'Create reusable Vapi tools and/or attach existing tool IDs' while explicitly noting that the current assistant model configuration is preserved. This distinguishes it from sibling tools like attach_phone and set_prompt_and_voice.

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: use this when you need to add or attach Vapi tools without changing the model configuration. However, it does not explicitly state when not to use it or mention alternative sibling tools for related workflows.

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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