Vapi - AI Voice Assistant Builder

Build AI-powered voice assistants, phone agents, and conversational AI applications with Vapi.

Workflow

1. Check for the Vapi MCP Server

Check whether a Vapi MCP server is connected by discovering tools such as list_assistants. MCP hosts may namespace displayed tool names with the configured server name.

If the server is unavailable, tell the user to configure one of these supported connections in their MCP host:

• Local stdio command: npx -y @vapi-ai/mcp-server, with VAPI_TOKEN set in the server environment
• Remote Streamable HTTP: https://mcp.vapi.ai/mcp, with an Authorization: Bearer <VAPI_TOKEN> header

Tell the user to reload or restart their MCP host if it requires that after configuration.

2. Confirm Vapi Credentials

If a tool returns an authentication error, tell the user to configure a Vapi API key as VAPI_TOKEN for a local server or as the bearer token for the remote server. Then retry after reloading the connection if required by the host.

3. Build the Voice Assistant

Before creating an assistant, fetch the latest prompt engineering guidelines from the Prompt Guide.

Use these guidelines to craft effective voice assistant prompts based on what the user wants to build.

Available Tools

Assistants

• list_assistants - List all assistants
• get_assistant - Get assistant details
• create_assistant - Create new assistant
• update_assistant - Update assistant

Calls

• list_calls - List call history
• get_call - Get call details
• create_call - Start outbound call

Phone Numbers

• list_phone_numbers - List phone numbers
• get_phone_number - Get phone number details

Tools (Function Calling)

• list_tools - List custom tools
• get_tool - Get tool details
• create_tool - Create tool for API integration
• update_tool - Update tool

Workflow Examples

User: "I want to build a voice assistant that can schedule appointments"

Agent workflow:

1. Check for Vapi MCP -> configure a connection if needed
2. Confirm VAPI_TOKEN is configured if the tools return authentication errors
3. Fetch the prompt guide for best practices
4. Ask about their business to understand context
5. Create an assistant with a scheduling-focused prompt
6. Help select an existing phone number, or direct the user to the Vapi dashboard to provision one
7. Help create calendar integration tools if needed

User: "Make me a phone bot that answers questions about my business"

Agent workflow:

1. Ensure Vapi MCP is connected and authenticated
2. Fetch the prompt guide for best practices
3. Ask about the business: name, services, hours, common questions
4. Craft a system prompt following the guidelines
5. Create the assistant
6. Help provision or connect a phone number
7. Offer to test with a sample call