slotSubscribe

Subscribe to receive notification anytime a slot is processed by the validator

Common use cases

Monitor blockchain progression in real-time	Track slot updates at the processed commitment level to detect when new blocks are produced. Essential for DeFi applications that need to time transactions or detect epoch boundaries for validator rewards and staking operations.
Implement RPC load balancing and validator health monitoring	Monitor multiple RPC endpoints simultaneously to detect the most up-to-date validator nodes and automatically route requests to nodes with the latest slot information. Helps maintain service reliability during network congestion or validator delays.
Detect transaction confirmation timing	Use slot progression to estimate when transactions will reach higher commitment levels. Slot notifications provide the foundational timing mechanism for tracking when processed transactions advance to confirmed and finalized states.

Parameters

No parameters required.

Request

wscat

wscat -c wss://solana-mainnet.api.syndica.io -x '{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "slotSubscribe"
}'

JavaScript

const ws = new WebSocket('wss://solana-mainnet.api.syndica.io');

ws.on('open', function open() {
  ws.send(JSON.stringify({
  "jsonrpc": "2.0",
  "id": 1,
  "method": "slotSubscribe"
}));
});

ws.on('message', function incoming(data) {
  console.log(data);
});

Python

import websocket
import json

ws = websocket.create_connection('wss://solana-mainnet.api.syndica.io')
ws.send(json.dumps({
  "jsonrpc": "2.0",
  "id": 1,
  "method": "slotSubscribe"
}))
result = ws.recv()
print(result)
ws.close()

Network Selection

Replace mainnet with devnet in the URL to query devnet instead.

Response

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

Response Fields

Return value: integer

Subscription id (needed to unsubscribe)

Notification Format

The notification will be an object with the following fields:

• parent: <u64> - The parent slot
• root: <u64> - The current root slot
• slot: <u64> - The newly set slot value

Example:

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

FAQ and Troubleshooting

Why doesn't slotSubscribe accept a commitment parameter?

slotSubscribe always uses 'processed' commitment level because it reports slots as soon as they are processed by the validator. This is the earliest commitment level and cannot be configured.

What's the difference between parent, root, and slot in the notification?

The 'slot' field is the current slot number, 'parent' is the previous slot, and 'root' is the most recent rooted (finalized) slot. All three are u64 integers representing slot heights.

How frequently will I receive slot notifications?

Notifications arrive approximately every 400-600ms during normal operation, matching Solana's target slot time of ~400ms. Actual timing varies based on network conditions and validator performance.

Should I use slotSubscribe or slotsUpdatesSubscribe?

Use slotSubscribe for simple slot progression monitoring at processed commitment. Use slotsUpdatesSubscribe when you need detailed slot lifecycle events including optimistic confirmations, frozen slots, and dead slot detection.

Related Methods

slotUnsubscribe
Cancels the slot subscription. Always call slotUnsubscribe when monitoring is no longer needed to free server resources and maintain proper WebSocket connection lifecycle.

slotsUpdatesSubscribe
Provides more detailed slot lifecycle events including optimistic confirmations, frozen slots, and dead slots. Use this instead of slotSubscribe when you need visibility into slot state transitions beyond basic progression.

blockSubscribe
Subscribe to block notifications with full transaction and account data. Complements slotSubscribe by providing block content once you've identified slots of interest through slot monitoring.

External Resources

• Solana Official Documentation