Monitor contract events

Track contract events and get event logs with the Circle Contracts API.

Prerequisites

You need a deployed contract to monitor. If you completed the Deploy contracts tutorial, you can continue with that contract. If your contract was deployed elsewhere, import it in Step 3.

Step 1. Update your project

If you haven’t already, add run scripts for monitoring contract events to your package.json:

npm pkg set scripts.webhook="tsx webhook-receiver.ts"
npm pkg set scripts.import-contract="tsx --env-file=.env import-contract.ts"
npm pkg set scripts.create-monitor="tsx --env-file=.env create-monitor.ts"
npm pkg set scripts.get-event-logs="tsx --env-file=.env get-event-logs.ts"

If you completed the Deploy contracts tutorial, your project already has the required SDKs installed. The npm scripts previously listed work with your existing setup.

Step 2. Set up your webhook

Event monitors send real-time updates to your webhook endpoint when events happen.

webhook.site
ngrok

Visit webhook.site
Copy your unique webhook URL (for example, https://webhook.site/your-uuid)

Install ngrok from ngrok.com
Create a webhook receiver script:

import express, { Request, Response } from "express";

const app = express();
app.use(express.json());

app.post("/webhook", (req: Request, res: Response) => {
  console.log("Received webhook:");
  console.log(JSON.stringify(req.body, null, 2));
  res.status(200).json({ received: true });
});

const PORT = 3000;
app.listen(PORT, () => {
  console.log(`Webhook receiver listening on port ${PORT}`);
  console.log(`Endpoint: http://localhost:${PORT}/webhook`);
});

Start the webhook receiver:

npm run webhook

In a separate terminal, start ngrok:

ngrok http 3000

Copy the HTTPS forwarding URL (for example, https://abc123.ngrok-free.app/webhook)

If using ngrok for local testing, you can optionally set WEBHOOK_URL in your .env file to store your ngrok forwarding URL.

Step 3. Register your webhook in Console

Go to Developer Console
Navigate to Webhooks (left sidebar)
Click Add a webhook
Enter your webhook URL (from Step 1) and create the webhook

Step 4. Import a contract (optional)

If your contract was deployed elsewhere and is not yet available in the Developer Console, import it first. If you deployed a contract using Circle Contracts, including the Deploy contracts tutorial, skip this step. Your contract is already available in the Console.

import { initiateSmartContractPlatformClient } from "@circle-fin/smart-contract-platform";

const contractClient = initiateSmartContractPlatformClient({
  apiKey: process.env.CIRCLE_API_KEY,
  entitySecret: process.env.CIRCLE_ENTITY_SECRET,
});

async function importContract() {
  try {
    const response = await contractClient.importContract({
      blockchain: "ARC-TESTNET",
      address: process.env.CONTRACT_ADDRESS,
      name: "MyContract",
    });

    console.log(JSON.stringify(response.data, null, 2));
  } catch (error) {
    console.error("Error importing contract:", error.message);
    throw error;
  }
}

importContract();

Run the script:

npm run import-contract

If the contract is already imported, you’ll see an error: contract already exists. This means the contract is already available in the Console and you can proceed to create an event monitor.

Step 5. Create an event monitor

Event monitors track specific contract events. They send updates to your webhook endpoint. This example monitors Transfer events:

import { initiateSmartContractPlatformClient } from "@circle-fin/smart-contract-platform";

const contractClient = initiateSmartContractPlatformClient({
  apiKey: process.env.CIRCLE_API_KEY,
  entitySecret: process.env.CIRCLE_ENTITY_SECRET,
});

async function createEventMonitor() {
  try {
    const response = await contractClient.createEventMonitor({
      blockchain: "ARC-TESTNET",
      contractAddress: process.env.CONTRACT_ADDRESS,
      eventSignature: "Transfer(address,address,uint256)",
    });

    console.log(JSON.stringify(response.data, null, 2));
  } catch (error) {
    console.error("Error creating event monitor:", error.message);
    throw error;
  }
}

createEventMonitor();

Run the script:

npm run create-monitor

Response:

{
  "eventMonitor": {
    "id": "019bf984-b4da-7026-a3d2-674ce371a933",
    "contractName": "TestERC20Token",
    "contractId": "019bf8be-7be5-7a3e-89cc-05bcd7413f20",
    "contractAddress": "0x281156899e5bd6fecf1c0831ee24894eeeaea2f8",
    "blockchain": "ARC-TESTNET",
    "eventSignature": "Transfer(address,address,uint256)",
    "eventSignatureHash": "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef",
    "isEnabled": true,
    "createDate": "2026-01-26T08:56:22.490638Z",
    "updateDate": "2026-01-26T08:56:22.490638Z"
  }
}

Step 6. Receive webhook notifications

When events occur, Circle sends updates to your endpoint. Here is what a Transfer event looks like:

{
  "subscriptionId": "f0332621-a117-4b7b-bdf0-5c61a4681826",
  "notificationId": "5c5eea9f-398f-426f-a4a5-1bdc28b36d2c",
  "notificationType": "contracts.eventLog",
  "notification": {
    "contractAddress": "0x4abcffb90897fe7ce86ed689d1178076544a021b",
    "blockchain": "ARC-TESTNET",
    "txHash": "0xe15d6dbb50178f60930b8a3e3e775f3c022505ea2e351b6c2c2985d2405c8ebc",
    "userOpHash": "0x78c3e8185ff9abfc7197a8432d9b79566123616c136001e609102c97e732e55e",
    "blockHash": "0x0ad6bf57a110d42620defbcb9af98d6223f060de588ed96ae495ddeaf3565c8d",
    "blockHeight": 22807198,
    "eventSignature": "Transfer(address,address,uint256)",
    "eventSignatureHash": "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef",
    "topics": [
      "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef",
      "0x0000000000000000000000000000000000000000000000000000000000000000",
      "0x000000000000000000000000bcf83d3b112cbf43b19904e376dd8dee01fe2758"
    ],
    "data": "0x0000000000000000000000000000000000000000000000000de0b6b3a7640000",
    "firstConfirmDate": "2026-01-21T06:53:12Z"
  },
  "timestamp": "2026-01-21T06:53:13.194467201Z",
  "version": 2
}

Key fields:

notificationType: Always "contracts.eventLog" for event monitor webhooks
notification.eventSignature: The event that was emitted
notification.contractAddress: Address of the contract that emitted the event
notification.blockchain: The blockchain network (for example, ARC-TESTNET)
notification.txHash: Transaction hash where the event occurred
notification.userOpHash: User operation hash (for smart contract accounts)
notification.blockHash: Hash of the block containing the transaction
notification.blockHeight: Block number where the event occurred
notification.eventSignatureHash: Keccak256 hash of the event signature
notification.topics: Indexed event parameters (for example, from and to addresses)
notification.data: Non-indexed event parameters (for example, token amount)
notification.firstConfirmDate: Timestamp when the event was first confirmed
timestamp: Timestamp when the webhook was sent
version: Webhook payload version

You can verify webhook delivery status in the Developer Console under Contracts → Monitoring.

Step 7. Retrieve event logs

You can also query event logs with the API. This is useful for past events or if you prefer polling.

Webhooks vs Polling: Webhooks send real-time updates (push). Polling needs periodic API calls (pull). Use webhooks for production and polling for testing or past queries.

import { initiateSmartContractPlatformClient } from "@circle-fin/smart-contract-platform";

const contractClient = initiateSmartContractPlatformClient({
  apiKey: process.env.CIRCLE_API_KEY,
  entitySecret: process.env.CIRCLE_ENTITY_SECRET,
});

async function getEventLogs() {
  try {
    const response = await contractClient.listEventLogs({
      contractAddress: process.env.CONTRACT_ADDRESS,
      blockchain: "ARC-TESTNET",
      pageSize: 10,
    });

    console.log(JSON.stringify(response.data, null, 2));
  } catch (error) {
    console.error("Error fetching event logs:", error.message);
    throw error;
  }
}

getEventLogs();

Run the script:

npm run get-event-logs

Replace CONTRACT_ADDRESS with your contract address. You can get this address when you deploy the contract, or by listing your contracts with listContracts().

Response:

{
  "eventLogs": [
    {
      "id": "019bf987-f901-7145-9e95-55f177b05b24",
      "subscriptionId": "019bf984-b4da-7026-a3d2-674ce371a933",
      "contractId": "019bf8be-7be5-7a3e-89cc-05bcd7413f20",
      "contractName": "TestERC20Token",
      "blockchain": "ARC-TESTNET",
      "txHash": "0x3bfbab5d5ce0d1a5d682cbc742d3940cf59db0369d173b71ba2a3b8f43bfbcb1",
      "logIndex": "50",
      "blockHash": "0x7d12148f9331556b31f84f58a41b7ff16eaaa47940f9e86733037d7ab74d858e",
      "blockHeight": 23686153,
      "contractAddress": "0x281156899e5bd6fecf1c0831ee24894eeeaea2f8",
      "eventSignature": "Transfer(address,address,uint256)",
      "eventSignatureHash": "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef",
      "topics": [
        "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef",
        "0x0000000000000000000000000000000000000000000000000000000000000000",
        "0x000000000000000000000000bcf83d3b112cbf43b19904e376dd8dee01fe2758"
      ],
      "data": "0x0000000000000000000000000000000000000000000000000de0b6b3a7640000",
      "decodedTopics": null,
      "decodedData": null,
      "userOpHash": "0x66befac1a371fcdddf1566215e4677127e111dff9253f306f7096fed8642a208",
      "firstConfirmDate": "2026-01-26T08:59:55Z",
      "createDate": "2026-01-26T08:59:56.545962Z",
      "updateDate": "2026-01-26T08:59:56.545962Z"
    }
  ]
}

You can view, update, and delete event monitors with the Circle Contracts API. See the API Reference for details on managing your monitors.

Summary

After completing this tutorial, you’ve successfully:

Set up webhook endpoints using webhook.site or ngrok
Registered webhooks in the Developer Console
Created event monitors for specific contract events
Received real-time webhook updates for contract events
Retrieved past event logs with the Circle SDK

Get Started

Build on Arc

References

Key Features

Architecture

Tools

Build AI Agents

Monitor contract events

Prerequisites

Step 1. Update your project

Step 2. Set up your webhook

Step 3. Register your webhook in Console

Step 4. Import a contract (optional)

Step 5. Create an event monitor

Step 6. Receive webhook notifications

Step 7. Retrieve event logs

Summary

Get Started

Build on Arc

References

Key Features

Architecture

Tools

Build AI Agents

​Prerequisites

​Step 1. Update your project

​Step 2. Set up your webhook

​Step 3. Register your webhook in Console

​Step 4. Import a contract (optional)

​Step 5. Create an event monitor

​Step 6. Receive webhook notifications

​Step 7. Retrieve event logs

​Summary

Prerequisites

Step 1. Update your project

Step 2. Set up your webhook

Step 3. Register your webhook in Console

Step 4. Import a contract (optional)

Step 5. Create an event monitor

Step 6. Receive webhook notifications

Step 7. Retrieve event logs

Summary