slotSubscribe

The slotSubscribe method creates a subscription that delivers real-time notifications each time a validator processes a slot.

📘 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.
• This subscription fires a notification every time a validator processes a slot, which can result in a very high frequency of notifications.
• CU is consumed based on the volume of subscribed data. Use appropriate filtering options to subscribe only to the data you need.

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1. Request

Parameters

The slot 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 "slotSubscribe".
params	array	required	No additional parameters are required for slot subscription. Use an empty array.

Example

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "slotSubscribe",
  "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 slotUnsubscribe method.

Notifications

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

Notification format:

Field	Type	Description
parent	u64	The parent slot number
root	u64	The current root slot number
slot	u64	The newly processed slot number

Slot Notification Example

{
  "jsonrpc": "2.0",
  "method": "slotNotification",
  "params": {
    "result": {
      "parent": 75,
      "root": 44,
      "slot": 76
    },
    "subscription": 0
  }
}

---

3. How to Use

Connect to WebSocket Channel

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

Subscribe to Slots

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

Receive Notifications

• Initial response: a subscription ID is returned.
• Subsequent: a "slotNotification" event is received each time a validator processes a slot.

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 slotUnsubscribe to cancel a specific subscription while keeping the connection open.

Unsubscribe request:

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

Response after unsubscribing:

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