vapi-mcp-server

vapi_chat

Send a message to an AI assistant or resume an existing chat session for voice interactions.

Instructions

Send a message to an assistant or continue a chat session

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "vapi_chat"
  }
}

Input Schema

Name	Required	Description	Default
`assistantId`	No
`sessionId`	No
`messages`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Jun 21, 2026

TDQS

C2.7/5.0

Behavior2/5

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

No annotations are present, so the description must fully disclose behavioral traits. It states it sends a message but does not describe side effects, authorization requirements, whether it returns a reply, or how it behaves with missing parameters. This is insufficient for an agent to understand the tool's impact.

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

Conciseness4/5

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

The description is a single, concise sentence that front-loads the purpose. However, it compresses multiple concepts (sending vs continuing) without structure. It is efficient but could benefit from slight expansion for clarity.

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?

Given the lack of output schema, annotations, and low schema coverage, the description is incomplete. It does not explain return values, error conditions, or the format of the 'messages' parameter. An agent would struggle to invoke this tool correctly without additional context.

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?

Schema description coverage is 0%, so the description must add meaning. It does not clarify the structure of the 'messages' array, the relationship between 'assistantId' and 'sessionId', or any constraints. Only the param names are given, which provides minimal guidance.

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 verb and resource ('send a message', 'continue a chat session'). It distinguishes itself from sibling tools that are primarily CRUD or call management. However, it could more explicitly differentiate from 'create session' or 'end call' tools.

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 is provided on when to use this tool vs alternatives. It does not mention prerequisites (e.g., need an existing session or assistant), nor does it specify when not to use it. Siblings like 'vapi_create_session' and 'vapi_end_call' are related but no cross-referencing.

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