How to Monitor USDT Transactions Using go-ethereum

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Monitoring token transactions in real time is a common requirement in blockchain application development. This guide walks you through using the go-ethereum (geth) library to listen for USDT (Tether) transactions on the Ethereum network. We'll cover everything from setting up your Go environment to parsing event logs, handling reconnections, and optimizing for production use.

Whether you're building a wallet service, DeFi analytics tool, or transaction alert system, this tutorial provides a solid foundation for tracking ERC-20 transfers with precision and efficiency.

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Understanding USDT and ERC-20 Events

USDT is one of the most widely used stablecoins, issued on Ethereum as an ERC-20 token. The ERC-20 standard defines a set of functions and events that all compatible tokens must implement. One of the key events is Transfer, which fires every time USDT is sent from one address to another.

By listening to this event, developers can track all movements of USDT across the Ethereum blockchain in real time.

Key Details:

The indexed keyword allows us to filter logs by sender or receiver addresses directly at the node level, improving performance and reducing noise.

Prerequisites

Before diving into code, ensure you have:

  1. Go 1.16 or higher installed
  2. Access to an Ethereum node via WebSocket (wss://) — recommended services include Infura or Alchemy
  3. The go-ethereum library installed

No prior experience with smart contract event parsing is required, but familiarity with Go and basic blockchain concepts will help.

Step 1: Initialize Your Go Project

Start by creating a new module and installing the necessary dependency:

mkdir usdt-monitor
cd usdt-monitor
go mod init github.com/your-username/usdt-monitor
go get github.com/ethereum/go-ethereum

This sets up your workspace with access to Ethereum client functionality, including event subscription and ABI parsing.

Step 2: Define the USDT ABI

To interpret the raw log data, we need the Application Binary Interface (ABI) for the Transfer event. Since we only care about this specific event, we define a minimal ABI fragment:

const usdtABI = `[
  {
    "anonymous": false,
    "inputs": [
      { "indexed": true, "name": "from", "type": "address" },
      { "indexed": true, "name": "to", "type": "address" },
      { "indexed": false, "name": "value", "type": "uint256" }
    ],
    "name": "Transfer",
    "type": "event"
  }
]`

This compact definition enables us to decode event parameters without loading the full contract ABI.

Step 3: Connect to Ethereum via WebSocket

Real-time event listening requires a persistent connection. Use WebSocket (wss://) instead of HTTP:

client, err := ethclient.Dial("wss://mainnet.infura.io/ws/v3/YOUR_INFURA_PROJECT_ID")
if err != nil {
    log.Fatalf("Failed to connect: %v", err)
}
defer client.Close()
fmt.Println("Connected to Ethereum node")

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Step 4: Set Up the Event Filter

Create a filter query targeting the USDT contract and the Transfer event:

usdtContractAddress := common.HexToAddress("0xdAC17F958D2ee523a2206206994597C13D831ec7")

parsedABI, err := abi.JSON(strings.NewReader(usdtABI))
if err != nil {
    log.Fatalf("Failed to parse ABI: %v", err)
}

eventSignature := []byte("Transfer(address,address,uint256)")
eventID := crypto.Keccak256Hash(eventSignature)

query := ethereum.FilterQuery{
    Addresses: []common.Address{usdtContractAddress},
    Topics:    [][]common.Hash{{eventID}},
}

The Topics field uses the Keccak hash of the event signature to match only Transfer logs.

Step 5: Subscribe to Real-Time Logs

Use SubscribeFilterLogs to receive logs as they occur:

logs := make(chan types.Log)
sub, err := client.SubscribeFilterLogs(context.Background(), query, logs)
if err != nil {
    log.Fatalf("Subscription failed: %v", err)
}

fmt.Println("Monitoring USDT transfers...")

for {
    select {
    case err := <-sub.Err():
        log.Printf("Subscription error: %v", err)
        // Implement reconnection logic here
    case vLog := <-logs:
        event, err := parseTransferEvent(vLog, parsedABI)
        if err != nil {
            log.Printf("Error parsing log: %v", err)
            continue
        }
        fmt.Printf("Transfer: %s -> %s, Amount: %s USDT\n",
            event.From.Hex(),
            event.To.Hex(),
            formatUSDT(event.Value))
    }
}

Why Use SubscribeFilterLogs?

This method offers:

Unlike polling-based approaches, it avoids unnecessary requests and ensures near-instantaneous delivery.

Step 6: Parse and Format Event Data

Define a struct and helper functions to extract meaningful information:

type TransferEvent struct {
    From  common.Address
    To    common.Address
    Value *big.Int
}

func parseTransferEvent(log types.Log, contractABI abi.ABI) (*TransferEvent, error) {
    event := TransferEvent{}
    event.From = common.HexToAddress(log.Topics[1].Hex())
    event.To = common.HexToAddress(log.Topics[2].Hex())

    if len(log.Data) > 0 {
        err := contractABI.UnpackIntoInterface(&event.Value, "Transfer", log.Data)
        if err != nil {
            return nil, err
        }
    }

    return &event, nil
}

func formatUSDT(value *big.Int) string {
    divisor := big.NewInt(1000000)
    quotient := new(big.Int).Div(value, divisor)
    remainder := new(big.Int).Mod(value, divisor)
    return fmt.Sprintf("%s.%06s", quotient.String(), fmt.Sprintf("%06s", remainder.String()))
}

This correctly handles USDT’s 6 decimal places for human-readable output.

Step 7: Handle Historical Data (Optional)

To backfill past transactions:

func getHistoricalTransfers(client *ethclient.Client, contractAddress common.Address, fromBlock, toBlock *big.Int) {
    query := ethereum.FilterQuery{
        FromBlock: fromBlock,
        ToBlock:   toBlock,
        Addresses: []common.Address{contractAddress},
        Topics:    [][]common.Hash{{eventID}},
    }

    logs, err := client.FilterLogs(context.Background(), query)
    if err != nil {
        log.Fatalf("Failed to fetch logs: %v", err)
    }

    for _, vLog := range logs {
        // Process each log...
    }
}

Useful for initializing databases or auditing previous activity.

Best Practices and Production Tips

Core Keywords

go-ethereum, USDT transaction monitoring, Ethereum event listener, ERC-20 Transfer event, Golang blockchain development, real-time token tracking, WebSocket Ethereum, smart contract event parsing

Frequently Asked Questions

Q: Can I use HTTP instead of WebSocket for real-time listening?
A: No. SubscribeFilterLogs only works over WebSocket (wss://). HTTP does not support push-based subscriptions.

Q: How do I filter transfers involving a specific wallet?
A: Include the address in the Topics array under the relevant index (position 1 for "from", 2 for "to").

Q: What happens if my connection drops?
A: Always implement reconnection logic and track processed blocks to avoid missing events during outages.

Q: Is this approach suitable for high-volume monitoring?
A: Yes, but consider batching database writes and using goroutines for parallel processing under heavy load.

Q: How accurate is the parsed data?
A: As long as the ABI matches the contract’s actual interface, parsing is 100% accurate.

Q: Can I monitor other ERC-20 tokens the same way?
A: Absolutely — just update the contract address and verify the token’s decimal count.

With this implementation, you now have a robust system for tracking USDT movements on Ethereum. From here, you can extend functionality to support multiple tokens, integrate alerting systems, or build dashboards for transaction analytics.

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