vapi-mcp-server

vapi_create_call

Create a new Vapi call by providing an assistant ID, with optional phone number and customer information.

Instructions

Initiate a new Vapi call

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": {
      "assistantId": "<assistantId>"
    },
    "name": "vapi_create_call"
  }
}

Input Schema

Name	Required	Description	Default
`assistantId`	Yes
`phoneNumberId`	No
`customer`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Jun 21, 2026

TDQS

C2.2/5.0

Behavior1/5

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

With no annotations, the description carries full burden for behavioral disclosure. 'Initiate a new Vapi call' gives no information about side effects (e.g., cost, required preconditions, mutability). This is a significant gap.

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

Conciseness3/5

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

The description is a single sentence, which is concise, but it sacrifices necessary detail. It is not structured with front-loaded key information; it is too brief to be fully effective.

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?

Given the tool has 3 parameters (one nested), no output schema, and no annotations, the description is severely incomplete. It does not explain return values, error handling, or dependencies, making it inadequate for informed use.

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%, so the description must compensate but does not. Parameters (assistantId, phoneNumberId, customer) are not explained, leaving the agent without semantic understanding of required inputs.

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 'Initiate a new Vapi call' clearly specifies the action (initiate) and resource (call), distinguishing it from read tools like vapi_get_call or list tools like vapi_list_calls. However, it does not elaborate on the nature of the call (e.g., AI call, voice call), which limits specificity.

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?

No guidance provided on when to use this tool versus siblings like vapi_create_session or vapi_chat. The description lacks context for selecting this tool over alternatives.

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