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The Streams API enables you to stream real-time blockchain data to your application through webhooks. This tutorial focuses on monitoring wallet transactions as they happen on-chain. Common use cases include:
  • Web3 alerts (e.g. whale alerts monitoring)
  • Real-time transaction and crypto wallet notifications
  • Monitoring wallet balances

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Prerequisites

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Step 1: Install the Moralis SDK

Install the Moralis SDK for your preferred language:
npm
npm install moralis @moralisweb3/common-evm-utils
yarn
yarn add moralis @moralisweb3/common-evm-utils
pip
pip install moralis

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Step 2: Create a Stream to Monitor Wallet Transactions

Once you have your API key and webhook URL, set up a stream to monitor on-chain wallet transactions. In this example, we will monitor the address 0x68b3f12d6e8d85a8d3dbbc15bba9dc5103b888a4. JavaScript:
index.js
const Moralis = require("moralis").default;
const { EvmChain } = require("@moralisweb3/common-evm-utils");

const runApp = async () => {
  await Moralis.start({
    apiKey: "YOUR_API_KEY",
  });

  const stream = {
    chains: [EvmChain.ETHEREUM, EvmChain.POLYGON],
    description: "monitor Bobs wallet",
    tag: "bob",
    webhookUrl: "https://YOUR_WEBHOOK_URL",
    includeNativeTxs: true,
  };

  const newStream = await Moralis.Streams.add(stream);
  const { id } = newStream.toJSON();

  // Now we attach bobs address to the stream
  const address = "0x68b3f12d6e8d85a8d3dbbc15bba9dc5103b888a4";

  await Moralis.Streams.addAddress({ address, id });
};

runApp();
TypeScript:
index.ts
import Moralis from "moralis";
import { EvmChain } from "@moralisweb3/common-evm-utils";

const runApp = async () => {
  await Moralis.start({
    apiKey: "YOUR_API_KEY",
  });

  const stream = {
    chains: [EvmChain.ETHEREUM, EvmChain.POLYGON],
    description: "monitor Bobs wallet",
    tag: "bob",
    webhookUrl: "https://YOUR_WEBHOOK_URL",
    includeNativeTxs: true,
  };

  const newStream = await Moralis.Streams.add(stream);
  const { id } = newStream.toJSON();

  // Now we attach bobs address to the stream
  const address = "0x68b3f12d6e8d85a8d3dbbc15bba9dc5103b888a4";

  await Moralis.Streams.addAddress({ address, id });
};

runApp();
Python:
index.py
from moralis import streams

api_key = "YOUR_API_KEY"

create_stream_body = {
  "description": "monitor Bobs wallet",
  "tag": "bob",
  "webhook_url": "https://YOUR_WEBHOOK_URL",
  "include_native_txs": True,
  "chain_ids": [
    "0x1",
    "0x89"
  ]
}

result = streams.evm_streams.create_stream(
  api_key=api_key,
  body=create_stream_body,
)

add_address_body = {
  "address": "0x68b3f12d6e8d85a8d3dbbc15bba9dc5103b888a4"
}

params = {
  "id": result.id
}

# Now we attach bobs address to the stream
streams.evm_streams.add_address_to_stream(
  api_key=api_key,
  body=add_address_body,
  params=params,
)
Once the code has been added, run the script to create the stream. This will be reflected on your Moralis Dashboard as well. From here, you will receive new real-time responses on your attached webhook for any new transactions occurring on either Ethereum or Polygon.

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Step 3: Listen to Smart Contract Events

In addition to monitoring wallet transactions in real-time, you can use Streams to listen to smart contract events whenever they are emitted on the blockchain. For example, to listen to all ERC20 transfers for USDT: JavaScript:
index.js
const Moralis = require("moralis").default;
const { EvmChain } = require("@moralisweb3/common-evm-utils");

const ERC20_transfer_ABI = [
  {
    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",
  },
];

const runApp = async () => {
  await Moralis.start({
    apiKey: "YOUR_API_KEY",
  });

  const stream = {
    chains: [EvmChain.ETHEREUM],
    description: "monitor USDT transfers",
    tag: "USDT",
    webhookUrl: "https://YOUR_WEBHOOK_URL",
    abi: ERC20_transfer_ABI,
    includeContractLogs: true,
    topic0: ["Transfer(address,address,uint256)"],
  };

  const newStream = await Moralis.Streams.add(stream);
  const { id } = newStream.toJSON();

  // Now we attach USDT address to the stream
  const address = "0xdAC17F958D2ee523a2206206994597C13D831ec7";

  await Moralis.Streams.addAddress({ address, id });
};

runApp();
Python:
index.py
from moralis import streams

api_key = "YOUR_API_KEY"

ERC20_transfer_ABI = [{
  "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",
}]

create_stream_body = {
  "description": "monitor USDT transfers",
  "tag": "USDT",
  "webhook_url": "https://YOUR_WEBHOOK_URL",
  "include_contract_logs": True,
  "chain_ids": [
    "0x1"
  ],
  "abi": ERC20_transfer_ABI,
  "topic0": ["Transfer(address,address,uint256)"]
}

result = streams.evm_streams.create_stream(
  api_key=api_key,
  body=create_stream_body,
)

add_address_body = {
  "address": "0xdAC17F958D2ee523a2206206994597C13D831ec7"
}

params = {
  "id": result.id
}

# Now we attach USDT address to the stream
streams.evm_streams.add_address_to_stream(
  api_key=api_key,
  body=add_address_body,
  params=params,
)

​
Step 4: Add Filters for Specific Use Cases

For listening to smart contracts, you can add the Filters feature to filter out results that only fulfill certain criteria. This is useful for specific use cases such as whale monitoring. For example, to monitor all USDT transactions on Ethereum over $1M: JavaScript:
index.js
const filter_ERC20 = {
  "and": [
    { "eq": ["from", "0x283af0b28c62c092c9727f1ee09c02ca627eb7f5"] },
    { "gt": ["value", "1000000000"] }, // Example of USDT (6 Decimals)
  ],
};

const runApp = async () => {
  const stream = {
    // same parameters as prior
    advancedOptions: [
      {
        topic0: "Transfer(address,address,uint256)",
        filter: filter_ERC20
      },
    ]
  };

  const newStream = await Moralis.Streams.add(stream);
  const { id } = newStream.toJSON();

  // Now we attach USDT address to the stream
  const address = "0xdAC17F958D2ee523a2206206994597C13D831ec7";

  await Moralis.Streams.addAddress({ address, id });
};

runApp();
Python:
index.py
filter_ERC20 = {
  "and": [
    { "eq": ["from", "0x283af0b28c62c092c9727f1ee09c02ca627eb7f5"] },
    { "gt": ["value", "1000000000"] },  # Example of USDT (6 Decimals)
  ],
}

create_stream_body = {
  # same parameters as prior
  "advanced_options": [
    {
      "topic0": "Transfer(address,address,uint256)",
      "filter": filter_ERC20
    }
  ]
}

result = streams.evm_streams.create_stream(
  api_key=api_key,
  body=create_stream_body,
)

add_address_body = {
  "address": "0xdAC17F958D2ee523a2206206994597C13D831ec7"
}

params = {
  "id": result.id
}

# Now we attach USDT address to the stream
streams.evm_streams.add_address_to_stream(
  api_key=api_key,
  body=add_address_body,
  params=params,
)
Once modified, you will only receive USDT transfers on Ethereum over $1M in real-time on your webhooks.