MCP Tool (voice)

The MCP Tool turns your voice agent into an MCP client. The agent connects to an external MCP server during the call, discovers its tools, and uses them in-flight — for custom business logic, proprietary APIs, or third-party integrations without writing custom tool code.

This page is about the MCP client side — your voice agent consuming external MCP servers mid-call. Looking for the other direction? thinnestAI is itself an MCP server that Claude Desktop, ChatGPT, and Cursor can talk to. See MCP Server.

How It Works

Caller: "Can you check my loyalty points balance?"
Agent: "Let me look that up for you."
-> Agent calls mcp_call with tool_name="get_loyalty_balance"
-> MCP server processes the request and returns the balance
Agent: "You have 2,450 loyalty points, which is worth $24.50 in rewards."

Configuration

{
  "mcpServerEnabled": true,
  "mcpServerUrl": "https://mcp.your-company.com",
  "mcpServerApiKey": "mcp_key_...",
  "mcpAutoDiscoverTools": true,
  "mcpAllowedTools": ["get_loyalty_balance", "create_ticket", "lookup_order"],
  "mcpTimeout": 10000
}

Setting	Type	Default	Description
`mcpServerEnabled`	boolean	`false`	Enable MCP integration
`mcpServerUrl`	string	—	MCP server URL
`mcpServerApiKey`	string	—	API key for authentication
`mcpAutoDiscoverTools`	boolean	`true`	Auto-discover available tools from the server
`mcpAllowedTools`	string[]	`[]`	Allowlist of tool names (empty = allow all)
`mcpTimeout`	integer	`10000`	Timeout in milliseconds

LLM Tool

Tool name: mcp_call Call any tool on the connected MCP server.

Parameters:
  tool_name: string (name of the MCP tool to call)
  parameters: string (JSON object of parameters)

Returns: JSON result from the MCP server

If the tool is not in the allowlist:

Returns: "Tool 'tool_name' is not in the allowed tools list."

Security

Allowlist: Use mcpAllowedTools to restrict which MCP tools the agent can call
Authentication: The mcpServerApiKey is sent as a Bearer token in the Authorization header
Timeout: Configurable per-call timeout prevents hanging calls

Example — Create Agent with MCP Integration

curl -X POST https://api.thinnest.ai/v1/agents \
  -H "Authorization: Bearer $THINNESTAI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Loyalty Program Agent",
    "model": "gpt-4o",
    "instructions": "You help callers with their loyalty program. Use the mcp_call tool to check balances, redeem points, and look up order history. Available tools: get_loyalty_balance, redeem_points, lookup_order.",
    "voiceEnabled": true,
    "transcriber": { "provider": "deepgram", "model": "nova-2-conversationalai" },
    "voice": { "provider": "deepgram", "voiceId": "aura-2-thalia-en" },
    "mcpServerEnabled": true,
    "mcpServerUrl": "https://mcp.your-company.com",
    "mcpServerApiKey": "mcp_key_...",
    "mcpAutoDiscoverTools": true,
    "mcpAllowedTools": ["get_loyalty_balance", "redeem_points", "lookup_order"],
    "mcpTimeout": 10000
  }'

Introduction

Getting Started

Voice Agents

Agent Capabilities

Channels

Quality & Oversight

Platform

MCP Tool (voice)

MCP Tool (voice)

How It Works

Configuration

LLM Tool

Security

Example — Create Agent with MCP Integration

​MCP Tool (voice)

​How It Works

​Configuration

​LLM Tool

​Security

​Example — Create Agent with MCP Integration

MCP Tool (voice)

How It Works

Configuration

LLM Tool

Security

Example — Create Agent with MCP Integration