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eth_subscribe

Subscribe to different Optimism event types like newHeads, logs, and syncing using WebSockets.

Creates a new subscription for desired events. Sends data as soon as it occurs.

Parameters

  • Event types- specifies the type of event to listen to (ex: new pending transactions, logs, etc.)
  • Optional params - optional parameters to include to describe the type of event to listen to (ex: address)

Returns

While the subscription is active, you will receive events formatted as an object described below:

  • Event Object:
    • jsonrpc: Always "2.0"
    • method: Always "eth_subscription"
    • params: An object with the following fields:
      • subscription: The subscription ID returned by the eth_subscribe call which created this subscription. This ID will be attached to all received events and can also be used to cancel the subscription using eth_unsubscribe
      • result: An object whose contents vary depending on the event type.

Event types

The following event types are accepted in all eth_subscribe WebSocket requests through your Alchemy endpoint. You can view the individual docs for example requests and responses.

Subscription TypeDescription
alchemy_minedTransactionsEmits full transaction objects or hashes that are mined on the network based on provided filters and block tags.
newHeadsEmits new blocks that are added to the blockchain.
[logs][ref:logs]Emits logs attached to a new block that match certain topic filters.

Request

// initiate websocket stream first
wscat -c wss://opt-mainnet.g.alchemy.com/v2/demo

// no param specification - return all mined txs  
{"jsonrpc":"2.0","id": 2, "method": "eth_subscribe", "params": ["alchemy_minedTransactions"]}

// Installation: npm install alchemy-sdk
import { Alchemy, Network } from "alchemy-sdk";

const settings = {
  apiKey: "demo", // Replace with your Alchemy API Key.
  network: Network.OPT_MAINNET, // Replace with your network.
};
const alchemy = new Alchemy(settings);

// Subscription for Alchemy's minedTransactions API
alchemy.ws.on(
  {
    method: "alchemy_pendingTransactions",
    toAddress: "vitalik.eth",
    fromAddress: "0xshah.eth",
  },
  (tx) => console.log(tx)
);

Result

{"id":1,"result":"0xf13f7073ddef66a8c1b0c9c9f0e543c3","jsonrpc":"2.0"}

// hashesOnly = true
{
  "jsonrpc": "2.0",
  "method": "eth_subscription",
  "params": {
    "result": {
			"removed": false
			"transaction": {
				"hash":"0xa8f2cf69e302da6c8100b80298ed77c37b6e75eed1177ca22acd5772c9fb9876",
			}
    },
    "subscription": "0xf13f7073ddef66a8c1b0c9c9f0e543c3"
  }
}


// hashesOnly = false
{
  "jsonrpc": "2.0",
  "method": "eth_subscription",
  "params": {
    "result": {
			"removed": false
			"transaction": {
	      "blockHash":"0xbe847be2bceb74e660daf96b3f0669d58f59dc9101715689a00ef864a5408f43",
				"blockNumber":"0x5b8d80",
				"hash":"0xa8f2cf69e302da6c8100b80298ed77c37b6e75eed1177ca22acd5772c9fb9876",
				"from":"0x2a9847093ad514639e8cdec960b5e51686960291",
				"gas":"0x4f588",
				"gasPrice":"0xc22a75840",
				"input":"0x000101d521928b4146",
				"nonce":"0x9a2",
				"r":"0xb5889c55a0ebbf86627524affc9c4fdedc4608bee7a0f9880b5ec965d58e4264",
				"s":"0x2da32e817e2483ec2199ec0121b93384ac820049a75e11b40d152fc7558a5d72",
				"to":"0xc7ed8919c70dd8ccf1a57c0ed75b25ceb2dd22d1",
				"transactionIndex":"0x14",
				"type":"0x0",
				"v":"0x1c",
				"value":"0x0"
			}
    },
    "subscription": "0xf13f7073ddef66a8c1b0c9c9f0e543c3"
  }
}

WebSocket Limits

  • There is a limit of 20,000 WebSocket connections per API Key as well as 1,000 parallel WebSocket subscriptions per WebSocket connection, creating a maximum of 20 million subscriptions per application.
    • The maximum size of a JSON-RPC batch request that can be sent over a WebSocket connection is 20
    • Free tier users will be limited to 10 concurrent requests per WebSocket connection.
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