Vapi Tool Creation Create tools that give voice assistants the ability to take actions during calls — look up data, book appointments, transfer calls, send messages, and more. Setup: Ensure VAPI_API_KEY is set. See the setup-api-key skill if needed. Quick Start Create a Function Tool (cURL) curl -X POST https://api.vapi.ai/tool \ -H "Authorization: Bearer $VAPI_API_KEY " \ -H "Content-Type: application/json" \ -d '{ "type": "function", "function": { "name": "get_weather", "description": "Get current weather for a location", "parameters": { "type": "object", "properties": { "location": { "type": "string", "description": "City name, e.g. San Francisco" } }, "required": ["location"] } }, "server": { "url": "https://your-server.com/api/tools" } }' TypeScript (Server SDK) import { VapiClient } from "@vapi-ai/server-sdk" ; const vapi = new VapiClient ( { token : process . env . VAPI_API_KEY ! } ) ; const tool = await vapi . tools . create ( { type : "function" , function : { name : "get_weather" , description : "Get current weather for a location" , parameters : { type : "object" , properties : { location : { type : "string" , description : "City name, e.g. San Francisco" , } , } , required : [ "location" ] , } , } , server : { url : "https://your-server.com/api/tools" , } , } ) ; console . log ( "Tool created:" , tool . id ) ; Tool Types Function Tool The most common tool type. Your server receives the function call and returns a result. { "type" : "function" , "function" : { "name" : "lookup_order" , "description" : "Look up order status by order number" , "parameters" : { "type" : "object" , "properties" : { "orderNumber" : { "type" : "string" , "description" : "The order number to look up" } } , "required" : [ "orderNumber" ] } } , "server" : { "url" : "https://your-server.com/api/tools" } , "messages" : [ { "type" : "request-start" , "content" : "Let me look that up for you..." } , { "type" : "request-complete" , "content" : "I found your order information." } , { "type" : "request-failed" , "content" : "I'm having trouble looking that up. Let me try again." } ] } Transfer Call Tool Transfer the caller to another number or SIP endpoint. { "type" : "transferCall" , "destinations" : [ { "type" : "number" , "number" : "+1234567890" , "message" : "Transferring you to our billing department now." , "description" : "Transfer to billing department when customer has billing questions" } ] , "function" : { "name" : "transfer_to_billing" , "description" : "Transfer the caller to the billing department" } } SIP transfer: { "type" : "transferCall" , "destinations" : [ { "type" : "sip" , "sipUri" : "sip:billing@company.com" , "description" : "Transfer to billing via SIP" } ] } End Call Tool Allows the assistant to end the call programmatically. { "type" : "endCall" , "function" : { "name" : "end_call" , "description" : "End the call when the conversation is complete" } } DTMF Tool Send DTMF tones (touch-tone signals) during a call for IVR navigation. { "type" : "dtmf" , "function" : { "name" : "press_digits" , "description" : "Press phone keypad digits to navigate phone menus" , "parameters" : { "type" : "object" , "properties" : { "digits" : { "type" : "string" , "description" : "Digits to press (0-9, *, #)" } } , "required" : [ "digits" ] } } } Voicemail Tool Detect and handle voicemail. { "type" : "voicemail" , "function" : { "name" : "leave_voicemail" , "description" : "Leave a voicemail message" } } Google Calendar Tool { "type" : "google.calendar.event.create" , "function" : { "name" : "create_calendar_event" , "description" : "Schedule a meeting on Google Calendar" } } Google Sheets Tool { "type" : "google.sheets.row.append" , "function" : { "name" : "log_to_sheet" , "description" : "Log call data to a Google Sheet" } } Slack Tool { "type" : "slack.message.send" , "function" : { "name" : "notify_slack" , "description" : "Send a notification to Slack" } } MCP Tool Connect to Model Context Protocol servers. { "type" : "mcp" , "server" : { "url" : "https://your-mcp-server.com" } } Tool Server Implementation When the assistant calls a tool, Vapi sends a POST request to your server URL. Request Format { "message" : { "type" : "tool-calls" , "toolCallList" : [ { "id" : "call_abc123" , "name" : "get_weather" , "arguments" : { "location" : "San Francisco" } } ] , "call" : { "id" : "call-uuid" , "orgId" : "org-uuid" , "type" : "webCall" } } } Response Format Your server must return: { "results" : [ { "toolCallId" : "call_abc123" , "result" : "San Francisco: 65°F, partly cloudy" } ] } Example Server (Express.js) import express from "express" ; const app = express ( ) ; app . use ( express . json ( ) ) ; app . post ( "/api/tools" , async ( req , res ) => { const { message } = req . body ; const results = [ ] ; for ( const toolCall of message . toolCallList ) { let result : string ; switch ( toolCall . name ) { case "get_weather" : const weather = await fetchWeather ( toolCall . arguments . location ) ; result = ${ toolCall . arguments . location } : ${ weather . temp } °F, ${ weather . condition } ; break ; case "lookup_order" : const order = await lookupOrder ( toolCall . arguments . orderNumber ) ; result = Order ${ order . number } : ${ order . status } ; break ; default : result = "Unknown tool" ; } results . push ( { toolCallId : toolCall . id , result } ) ; } res . json ( { results } ) ; } ) ; app . listen ( 3000 ) ; Attaching Tools to Assistants By tool ID (recommended for reusable tools) curl -X PATCH https://api.vapi.ai/assistant/ { assistant-id } \ -H "Authorization: Bearer $VAPI_API_KEY " \ -H "Content-Type: application/json" \ -d '{ "model": { "provider": "openai", "model": "gpt-4.1", "toolIds": ["tool-id-1", "tool-id-2"], "messages": [{"role": "system", "content": "Your prompt here"}] } }' Inline (for one-off tools) Define tools directly in the assistant's model configuration — see the create-assistant skill. Managing Tools

List all tools

curl https://api.vapi.ai/tool -H "Authorization: Bearer $VAPI_API_KEY "

Get a tool

curl https://api.vapi.ai/tool/ { id } -H "Authorization: Bearer $VAPI_API_KEY "

Update a tool

curl -X PATCH https://api.vapi.ai/tool/ { id } \ -H "Authorization: Bearer $VAPI_API_KEY " \ -H "Content-Type: application/json" \ -d '{"function": {"description": "Updated description"}}'

Delete a tool

curl -X DELETE https://api.vapi.ai/tool/ { id } \ -H "Authorization: Bearer $VAPI_API_KEY " Async Tools For long-running operations, mark a tool as async. The assistant continues speaking while the tool executes: { "type" : "function" , "async" : true , "function" : { "name" : "send_email" , "description" : "Send a confirmation email (runs in background)" } , "server" : { "url" : "https://your-server.com/api/tools" } } Tool Messages Control what the assistant says during tool execution: { "messages" : [ { "type" : "request-start" , "content" : "One moment while I look that up..." } , { "type" : "request-complete" , "content" : "Got it!" } , { "type" : "request-failed" , "content" : "Sorry, I couldn't complete that action." } , { "type" : "request-response-delayed" , "content" : "This is taking a bit longer than usual, please hold." , "timingMilliseconds" : 5000 } ] } References Tool Server Implementation — Detailed server setup guide Vapi Tools Docs — Official documentation Additional Resources This skills repository includes a Vapi documentation MCP server ( vapi-docs ) that gives your AI agent access to the full Vapi knowledge base. Use the searchDocs tool to look up anything beyond what this skill covers — advanced configuration, troubleshooting, SDK details, and more. Auto-configured: If you cloned or installed these skills, the MCP server is already configured via .mcp.json (Claude Code), .cursor/mcp.json (Cursor), or .vscode/mcp.json (VS Code Copilot). Manual setup: If your agent doesn't auto-detect the config, run: claude mcp add vapi-docs -- npx -y mcp-remote https://docs.vapi.ai/_mcp/server See the README for full setup instructions across all supported agents.