Setup Webhook

Vapi Webhook / Server URL Setup

Configure server URLs to receive real-time events from Vapi during calls — transcripts, tool calls, status changes, and end-of-call reports.

Setup: Ensure VAPI_API_KEY is set. See the setup-api-key skill if needed.

Overview

Vapi uses "Server URLs" (webhooks) to communicate with your application. Unlike traditional one-way webhooks, Vapi server URLs support bidirectional communication — your server can respond with data that affects the call.

Where to Set Server URLs

On an Assistant

curl -X PATCH https://api.vapi.ai/assistant/{id} \
  -H "Authorization: Bearer $VAPI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "server": {
      "url": "https://your-server.com/vapi/webhook",
      "credentialId": "cred_abc123"
    }
  }'

Create the optional credentialId in Dashboard > Custom Credentials. Omit it only for a deliberately public endpoint.

On a Phone Number

Phone-number updates also use a server object with url and optional credentialId. When updating through the API, first retrieve the number and preserve its existing provider discriminator in the PATCH body. The dashboard is the safest choice when the provider is unknown.

At the Organization Level

Set a default server URL in the Vapi Dashboard under Settings > Server URL.

Priority order: Tool server URL > Assistant server URL > Phone Number server URL > Organization server URL.

Event Types

Webhook Server Example (Express.js)

import express from "express";
const app = express();
app.use(express.json());

app.post("/vapi/webhook", (req, res) => {
  const { message } = req.body;

  switch (message.type) {
    case "assistant-request":
      // Dynamically configure the assistant based on the caller
      res.json({
        assistant: {
          name: "Dynamic Assistant",
          firstMessage: `Hello ${message.call.customer?.name || "there"}!`,
          model: {
            provider: "openai",
            model: "gpt-4.1",
            messages: [
              { role: "system", content: "You are a helpful assistant." },
            ],
          },
          voice: { provider: "vapi", voiceId: "Elliot", version: 2 },
          transcriber: { provider: "deepgram", model: "nova-3", language: "en" },
        },
      });
      break;

    case "tool-calls":
      // Handle tool calls from the assistant
      const results = (message.toolCallList || []).map((toolCall: any) => ({
        toolCallId: toolCall.id,
        result: handleToolCall(
          toolCall.name,
          toolCall.parameters || toolCall.arguments
        ),
      }));
      res.json({ results });
      break;

    case "end-of-call-report":
      // Process the call report
      console.log("Call ended:", {
        callId: message.call.id,
        endedReason: message.endedReason,
        cost: message.cost,
        analysis: message.analysis,
        artifact: message.artifact,
      });
      res.json({});
      break;

    case "status-update":
      console.log("Call status:", message.status);
      res.json({});
      break;

    case "transcript":
      console.log(`[${message.role}]: ${message.transcript}`);
      res.json({});
      break;

    default:
      res.json({});
  }
});

function handleToolCall(name: string, args: any): string {
  // Implement your tool logic here
  return `Result for ${name}`;
}

app.listen(3000, () => console.log("Webhook server running on port 3000"));

Webhook Server Example (Python / Flask)

from flask import Flask, request, jsonify

app = Flask(__name__)

@app.route("/vapi/webhook", methods=["POST"])
def vapi_webhook():
    data = request.json
    message = data.get("message", {})
    msg_type = message.get("type")

    if msg_type == "assistant-request":
        return jsonify({
            "assistant": {
                "name": "Dynamic Assistant",
                "firstMessage": "Hello! How can I help?",
                "model": {
                    "provider": "openai",
                    "model": "gpt-4.1",
                    "messages": [
                        {"role": "system", "content": "You are a helpful assistant."}
                    ],
                },
                "voice": {"provider": "vapi", "voiceId": "Elliot", "version": 2},
                "transcriber": {"provider": "deepgram", "model": "nova-3", "language": "en"},
            }
        })

    elif msg_type == "tool-calls":
        results = []
        for tool_call in message.get("toolCallList", []):
            results.append({
                "toolCallId": tool_call["id"],
                "result": f"Handled {tool_call['name']}",
            })
        return jsonify({"results": results})

    elif msg_type == "end-of-call-report":
        print(f"Call ended: {message['call']['id']}")
        print(f"Summary: {message.get('analysis', {}).get('summary')}")

    return jsonify({})

if __name__ == "__main__":
    app.run(port=3000)

Webhook Authentication

Use a Vapi Custom Credential and place its ID in server.credentialId. Vapi supports Bearer Token, OAuth 2.0 client credentials, and HMAC credentials. Verify requests according to the credential you configured; HMAC header names, algorithms, timestamps, and payload formats are configurable, so do not assume a fixed x-vapi-signature format.

For a bearer credential, compare the incoming Authorization: Bearer <token> value with the token stored securely by your server. Never put the secret itself in an assistant or phone-number payload.

Local Development

Use the Vapi CLI with a public tunnel. The CLI forwards from port 4242 to your app, but it does not create the public URL itself:

# Install the CLI
curl -sSL https://vapi.ai/install.sh | bash

# Terminal 1: expose the CLI listener
ngrok http 4242

# Terminal 2: forward events from the CLI to your app
vapi listen --forward-to localhost:3000/vapi/webhook

Set the Vapi server URL to the public ngrok URL. To skip the CLI and tunnel directly to the Express or Flask server instead:

ngrok http 3000
# Copy the ngrok URL and set it as your server URL

End-of-Call Report Fields

The end-of-call-report event includes:

References

• Common Server URL Events — Common event payloads and responses
• Setting Server URLs — Placement and priority
• Server Authentication — Custom Credentials
• Local Development — Testing webhooks locally

Additional Resources

Vapi provides a documentation MCP server that gives compatible AI agents access to the Vapi knowledge base. Use its documentation search for advanced configuration, troubleshooting, SDK details, and anything beyond this skill.

See the Vapi MCP integration guide for setup instructions across supported agents.