slotsUpdatesSubscribe

The slotsUpdatesSubscribe method creates a subscription that delivers real-time notifications for various types of updates occurring in each slot as processed by a validator.

📘 Usage Notes

• This method must be called via a WebSocket endpoint. HTTP is not supported.
• If the WebSocket connection is dropped, the subscription is automatically cancelled. Re-subscribe after reconnecting.
• CU is consumed based on the volume of subscribed data. Use appropriate filtering options to subscribe only to the data you need.

⚠️ This subscription may be unstable.

• This subscription receives various updates for each slot, which can result in a very high frequency of notifications.
• The subscription format is subject to change in the future and may not always be supported.

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1. Request

Parameters

The slot updates subscription request accepts the following parameters.

Parameter	Type	Required	Description
id	integer or string	required	A unique identifier for the request, used by the client to match requests with responses.
jsonrpc	string	required	The JSON-RPC protocol version. Always set to "2.0".
method	string	required	The name of the method to invoke. Set to "slotsUpdatesSubscribe".
params	array	required	No additional parameters are required for slot updates subscription. Use an empty array.

Example

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "slotsUpdatesSubscribe",
  "params": []
}

---

2. Response

Subscription Response

On success, the server returns a subscription ID.

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

This subscription ID is required when calling the slotsUpdatesUnsubscribe method.

Notifications

Once the subscription is active, the server pushes a notification each time a validator processes a slot update.

Notification format:

Field	Type	Description
err	string | undefined	Error message. Present only when the update type is "dead".
parent	u64 | undefined	Parent slot. Present only when the update type is "createdBank".
slot	u64	The newly updated slot number.
stats	object | undefined	Statistics information. Present only when the update type is "frozen".
stats.maxTransactionsPerEntry	u64 | undefined	Maximum number of transactions per entry.
stats.numFailedTransactions	u64 | undefined	Number of failed transactions.
stats.numSuccessfulTransactions	u64 | undefined	Number of successful transactions.
stats.numTransactionEntries	u64 | undefined	Number of transaction entries.
timestamp	i64	Unix timestamp of the update.
type	string	The update type. Returns one of: "firstShredReceived", "completed", "createdBank", "frozen", "dead", "optimisticConfirmation", "root"

Slots Updates Notification Example

{
  "jsonrpc": "2.0",
  "method": "slotsUpdatesNotification",
  "params": {
    "result": {
      "parent": 75,
      "slot": 76,
      "timestamp": 1625081266243,
      "type": "optimisticConfirmation"
    },
    "subscription": 0
  }
}

---

3. How to Use

Connect to WebSocket Channel

wscat -c wss://api.mainnet-beta.solana.com

Subscribe to Slots Updates

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "slotsUpdatesSubscribe",
  "params": []
}

Receive Notifications

• Initial response: a subscription ID is returned.
• Subsequent: a "slotsUpdatesNotification" event is received each time a slot update occurs.

Unsubscribe

There are two ways to cancel a subscription:

1. Close the connection: Press CTRL+C in the terminal to close the WebSocket connection. All active subscriptions are automatically cancelled.

2. Cancel a specific subscription: Use slotsUpdatesUnsubscribe to cancel a specific subscription while keeping the connection open.

Unsubscribe request:

{
  "jsonrpc": "2.0",
  "id": 2,
  "method": "slotsUpdatesUnsubscribe",
  "params": [0]
}

Response after unsubscribing:

{
  "jsonrpc": "2.0",
  "result": true,
  "id": 2
}