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slotSubscribe

Subscribes to slot progression and streams a notification each time the node processes a new slot.

Solanasol.pubsubbasic+ — per-method tier gating on /ws/sol

slotSubscribe is the cluster's heartbeat: it takes no parameters and pushes a slotNotification every time the serving node processes a new slot — roughly every 400 ms on a healthy cluster. Each notification carries three numbers: slot (the slot just processed), parent (the slot it builds on), and root (the newest rooted slot the node knows, i.e. the finalized watermark trailing a few dozen slots behind the tip).

It replaces polling getSlot in any latency-sensitive loop. Common uses: driving a "current slot" ticker in an explorer or dashboard; timestamping events from other subscriptions on the same socket; measuring your own pipeline lag by comparing the streamed tip against the slots your data arrives at; building blockhash-expiry countdowns for pending transactions; and acting as an application-level liveness signal — if slot notifications stall for more than a couple of seconds, the node or your connection is in trouble, which makes this the cheapest health probe a WebSocket session can carry.

Interpret the stream carefully. Slots arrive at the node's processed level, so the sequence tracks the tip of the fork the node is currently on — it is not a finality signal. The slot sequence is not guaranteed to be strictly consecutive from the client's point of view: skipped slots (leaders that produced no block) and minor fork switches mean you may observe gaps, and parent is how you stitch the true chain together. If you need to know when slots become final rather than merely processed, subscribe to rootSubscribe instead, or watch the root field here. For fine-grained per-slot lifecycle events (shreds received, banks frozen, dead slots), the heavier slotsUpdatesSubscribe exists. As with all Pub/Sub streams, a reconnect requires a fresh slotSubscribe; stop the stream with slotUnsubscribe.

Parameters

None — params is an empty array (or omitted).

Response

Subscribe ack:

Roughly every 400 ms thereafter:

{
  "jsonrpc": "2.0",
  "method": "slotNotification",
  "params": {
    "subscription": 3114,
    "result": {
      "parent": 348392040,
      "root": 348392008,
      "slot": 348392041
    }
  }
}
result (on ack)integer
Subscription id — pass it to slotUnsubscribe.
params.result.slotinteger
The newly processed slot.
params.result.parentinteger
Parent slot of slot.
params.result.rootinteger
Latest rooted (finalized) slot known to the node.

Errors

CodeMeaningWhen it happens
4003forbiddenYour tier is below basic (tier_insufficient).
4001unauthorizedMissing or invalid API key on the upgrade / auth frame.
4029rate_limitedSubscribe rate exceeded for your tier.

Notes

  • Processed, not final: the stream follows the node's current fork tip; use root (or rootSubscribe) for finality.
  • Gaps are normal: skipped slots and fork switches make the sequence non-consecutive; chain by parent when ordering matters.
  • ~2.5 frames/sec, forever: cheap individually, but unsubscribe when the consumer goes away.
  • Related methods: slotUnsubscribe, rootSubscribe, slotsUpdatesSubscribe, and getSlot for one-shot reads.