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Creates a real-time event subscription over a WebSocket connection. Returns a subscription ID; events are pushed as eth_subscription notifications without the client needing to poll.
The public Base endpoints (mainnet.base.org, sepolia.base.org) are HTTP only. WebSocket connections are not available on public Base endpoints — use a node provider such as Alchemy or QuickNode that offers WebSocket support for Base.

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Parameters

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subscriptionType
string
required
The event type to subscribe to.
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filterOptions
object
Optional filter options. Only applicable for the "logs" subscription type.

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Subscription Types

TypeDescriptionNotification payload
newHeadsFires for each new block appended to the chainFull block header object — identical shape to eth_getBlockByNumber with hydrated: false
logsFires for each new log matching filter criteriaLog object (see below)
newPendingTransactionsFires for each new transaction hash added to the mempoolTransaction hash string

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Returns

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result
string
A hex-encoded subscription ID. All event notifications from this subscription include this ID in params.subscription.
Event notifications arrive as unsolicited JSON-RPC messages: 
{
  "jsonrpc": "2.0",
  "method": "eth_subscription",
  "params": {
    "subscription": "0x1887ec8b9589ccad00000000000532da",
    "result": { ... }
  }
}

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Example

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