Event Listeners with TronWeb: Monitor TRC-20 Transfers on TRON

Real-time USDT deposit detection powers exchanges, payment gateways, and gaming platforms on TRON. Instead of polling balanceOf every second, production systems listen for Transfer events emitted by the USDT contract when funds arrive at monitored addresses.

This guide covers event mechanics, TronGrid queries, TronWeb patterns, and scalable architecture.

TRC-20 Transfer event

event Transfer(address indexed from, address indexed to, uint256 value);

Topic0 (event signature hash):

ddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef

Indexed from and to enable filtering by recipient — critical for deposit wallets.

USDT contract: TR7NHqjeKQxGTCi8q8ZY4pL8otSzgjLj6t

TronGrid events API

Pattern (check latest TronGrid docs for exact path):

GET /v1/contracts/{contractAddress}/events?event_name=Transfer&only_confirmed=true

Filter client-side or via API params for to address matching your deposit wallet.

Headers: TRON-PRO-API-KEY

Paginate with fingerprint for historical sync.

Polling worker example

const USDT = 'TR7NHqjeKQxGTCi8q8ZY4pL8otSzgjLj6t';
let lastTimestamp = Date.now() - 60_000;

async function pollTransfers(depositAddress) {
  const url = `https://api.trongrid.io/v1/contracts/${USDT}/events?event_name=Transfer&only_confirmed=true&min_block_timestamp=${lastTimestamp}`;
  const res = await fetch(url, {
    headers: { 'TRON-PRO-API-KEY': process.env.TRONGRID_KEY },
  });
  const { data } = await res.json();

  for (const ev of data || []) {
    const to = tronWeb.address.fromHex(ev.result.to);
    if (to !== depositAddress) continue;
    const value = Number(ev.result.value) / 1e6;
    await creditDeposit(ev.transaction_id, value, ev);
  }
  lastTimestamp = Date.now();
}

setInterval(() => pollTransfers(process.env.DEPOSIT_ADDRESS), 5000);

TronWeb contract events

const contract = await tronWeb.contract().at(USDT);
// Historical — depends on TronWeb version / node support
const events = await contract.Transfer().get({
  filters: { to: depositAddressHex },
  fromBlock: 0,
  toBlock: 'latest',
});

Support varies — TronGrid REST is more reliable for production indexers.

Per-user deposit addresses

Two patterns:

Event filter on to field works best with unique addresses.

Full payment flow: accept USDT payments API.

Idempotency

Key: transaction_id + event_index or log index

Before crediting:

1. Check DB for existing txid
2. Verify transaction SUCCESS
3. Confirm contract is official USDT
4. Credit user

Scaling

High volume:

• Run dedicated indexer consuming TronGrid or self-hosted event plugin
• Queue events to Kafka/RabbitMQ
• Horizontal workers with partition by address range
• Archive old cursors in Redis

Latency expectations

TRON ~3s block time → poll interval 3–5s reasonable. Faster UX shows "confirming" until N blocks solidified.

Scaling event indexing

At high volume, run a dedicated indexer storing events in PostgreSQL rather than polling TronGrid from request handlers. Dedupe by transactionId + logIndex. Handle chain reorganizations — rare on TRON but index blockNumber for replay logic.

Transfer event signature reference

USDT Transfer event topic0 (keccak256): ddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef. Filter topic2 for recipient address (padded to 32 bytes). Decode data field as uint256 amount. Getting padding wrong causes missed deposits — use TronWeb ABI decoder rather than manual hex slicing where possible.

Related guides

• Accept USDT payments API
• TronGrid API guide
• Verify transaction API
• TRON HTTP API reference

FAQ

What event does USDT emit on transfer?

TRC-20 Transfer(address indexed from, address indexed to, uint256 value) — topic0 is the keccak256 event signature hash.

Can TronWeb subscribe like WebSocket on Ethereum?

TRON tooling typically uses polling TronGrid event endpoints or running your own event plugin — not identical to eth_subscribe.

How far back can I query events?

TronGrid retains indexed events — use pagination for full history sync on new deploy.

Do internal transactions emit Transfer?

USDT transfer is standard TRC-20 call — appears in logs on success. Parse parent tx logs.

Fake USDT events?

Filter contract_address strictly — phishing tokens emit similarly named events from wrong contracts.