Reacting to real-time events from Avalanche smart contracts allows for immediate responses and automation, improving user experience and streamlining application functionality. It ensures that applications stay synchronized with the blockchain state. There are two primary methods for receiving these on-chain events:
  • WebSockets, using libraries like Ethers.js or Viem
  • Webhooks, which send structured event data directly to your app via HTTP POST.
Both approaches enable real-time interactions, but they differ drastically in their reliability, ease of implementation, and long-term maintainability. In this post, we break down why Webhooks are the better, more resilient choice for most Avalanche developers.

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Architecture Overview

The diagram below compares the two models side-by-side: wss_vs_webhooks WebSockets
  • The app connects to the Avalanche RPC API over WSS to receive raw log data.
  • It must decode logs, manage connection state, and store data locally.
  • On disconnection, it must re-sync via an external Data API or using standard eth_* RPC calls (e.g., eth_getLogs, eth_getBlockByNumber).
Note: WSS is a transport protocol—not real-time by itself. Real-time capabilities come from the availability of eth_subscribe, which requires node support.
Webhooks
  • The app exposes a simple HTTP endpoint.
  • Decoded event data is pushed directly via POST, including token metadata.
  • Built-in retries ensure reliable delivery, even during downtime.
Important: Webhooks have a 48-hour retry window. If your app is down for longer, you still need a re-sync strategy using eth_* calls to recover older missed events.

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Using WebSockets: Real-time but high maintenance

WebSockets allow you to subscribe to events using methods like eth_subscribe. These subscriptions notify your app in real-time whenever new logs, blocks, or pending transactions meet your criteria. 
import { createPublicClient, webSocket, formatUnits } from 'viem';
import { avalancheFuji } from 'viem/chains';
import { usdcAbi } from './usdc-abi.mjs'; // Ensure this includes the Transfer event

// Your wallet address (case-insensitive comparison)
const MY_WALLET = '0x8ae323046633A07FB162043f28Cea39FFc23B50A'.toLowerCase(); //Chrome

async function monitorTransfers() {
    try {
        // USDC.e contract address on Avalanche Fuji
        const usdcAddress = '0x5425890298aed601595a70AB815c96711a31Bc65';

        // Set up the WebSocket client for Avalanche Fuji
        const client = createPublicClient({
            chain: avalancheFuji,
            transport: webSocket('wss://api.avax-test.network/ext/bc/C/ws'),
        });

        // Watch for Transfer events on the USDC contract
        client.watchContractEvent({
            address: usdcAddress,
            abi: usdcAbi,
            eventName: 'Transfer',
            onLogs: (logs) => {
                logs.forEach((log) => {
                    const { from, to, value } = log.args;
                    const fromLower = from.toLowerCase();

                    // Filter for transactions where 'from' matches your wallet
                    if (fromLower === MY_WALLET) {
                        console.log('*******');
                        console.log('Transfer from my wallet:');
                        console.log(`From: ${from}`);
                        console.log(`To: ${to}`);
                        console.log(`Value: ${formatUnits(value, 6)} USDC`); // USDC has 6 decimals
                        console.log(`Transaction Hash: ${log.transactionHash}`);
                    }
                });
            },
            onError: (error) => {
                console.error('Event watching error:', error.message);
            },
        });

        console.log('Monitoring USDC Transfer events on Fuji...');
    } catch (error) {
        console.error('Error setting up transfer monitoring:', error.message);
    }
}

// Start monitoring
monitorTransfers();
The downside? If your connection drops, you lose everything in between. You’ll need to:
  • Set up a database to track the latest processed block and log index.
  • Correctly handling dropped connections and reconnection by hand can be challenging to get right.
  • Use eth_getLogs to re-fetch missed logs.
  • Decode and process raw logs yourself to rebuild app state. This requires extra infrastructure, custom recovery logic, and significant maintenance overhead.

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Webhooks: Resilient and developer-friendly

Webhooks eliminate the complexity of managing live connections. Instead, you register an HTTP endpoint to receive blockchain event payloads when they occur. Webhook payload example: 
{
  "eventType": "address_activity",
  "event": {
    "transaction": {
      "txHash": "0x1d8f...",
      "from": "0x3D3B...",
      "to": "0x9702...",
      "erc20Transfers": [
        {
          "valueWithDecimals": "110.56",
          "erc20Token": {
            "symbol": "USDt",
            "decimals": 6
          }
        }
      ]
    }
  }
}
You get everything you need:
  • Decoded event data
  • Token metadata (name, symbol, decimals)
  • Full transaction context
  • No extra calls. No parsing. No manual re-sync logic.

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Key Advantages of Webhooks

  • Reliable delivery with zero effort: Built-in retries ensure no missed events during downtime
  • Instant enrichment: Payloads contain decoded logs, token metadata, and transaction context
  • No extra infrastructure: No WebSocket connections, no DB, no external APIs
  • Faster development: Go from idea to production with fewer moving parts
  • Lower operational cost: Less compute, fewer network calls, smaller surface area to manage
If we compare using a table:
FeatureWebSockets (Ethers.js/Viem)Webhooks
Interruption HandlingManual; Requires complex custom logicAutomatic; Built-in queues & retries
Data RecoveryRequires DB + External API for re-syncHandled by provider; No re-sync logic needed
Dev ComplexityHigh; Error-prone custom resilience codeLow; Focus on processing incoming POST data
InfrastructureWSS connection + DB + Potential Data API costApplication API endpoint
Data IntegrityRisk of gaps if recovery logic failsHigh; Ensures eventual delivery
PayloadOften raw; Requires extra calls for contextTypically enriched and ready-to-use
Multiple addressesManual filtering or separate listeners per addressSupports direct configuration for multiple addresses
Listen to wallet addressesRequires manual block/transaction filteringCan monitor wallet addresses and smart contracts

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Summary

  • WebSockets offer real-time access to Avalanche data, but come with complexity: raw logs, reconnect logic, re-sync handling, and decoding responsibilities.
  • Webhooks flip the model: the data comes to you, pre-processed and reliable. You focus on your product logic instead of infrastructure.
  • If you want to ship faster, operate more reliably, and reduce overhead, Webhooks are the better path forward for Avalanche event monitoring.