All pending transactions — `mempool`

Subscribe to the mempool channel to receive an event for every pending (unconfirmed) transaction the moment it is seen. No address required. To follow the pending transactions of a single address instead, use history with pending: true.

{ "action": "subscribe", "channel": "mempool" }

Optional & native-value only

This stream is an optional feature and may not be available on every network. It covers native value only — gas is excluded and token transfers are invisible until a transaction is mined. Subscribing where pending tracking is unavailable succeeds, but no events arrive.

`mempool`

{
  "type": "mempool",
  "data": {
    "hash": "0x...",
    "from": "0x...",
    "to": "0x...",
    "value": "1000000000000000000",
    "nonce": "42",
    "input": "0x",
    "gas": "21000",
    "gas_price": "30000000000",
    "max_fee_per_gas": null,
    "max_priority_fee_per_gas": null,
    "type": "0",
    "chain_id": "1",
    "seen_at": 1740391012
  }
}

Field	Type	Description
`hash`	string	Transaction hash.
`from`	string	Sender.
`to`	string \| `null`	Recipient; `null` for a pending contract creation.
`value`	string	Native value moved, in wei.
`nonce`	string	Sender nonce.
`input`	string	Calldata — `"0x"` for a plain native transfer.
`gas`	string	Gas limit.
`gas_price`	string \| `null`	Legacy/effective gas price (wei), if present.
`max_fee_per_gas`	string \| `null`	EIP-1559 max fee per gas (wei), if present.
`max_priority_fee_per_gas`	string \| `null`	EIP-1559 priority fee per gas (wei), if present.
`type`	string \| `null`	Transaction type (`0` legacy, `1` EIP-2930, `2` EIP-1559), if reported.
`chain_id`	string \| `null`	Chain id, if reported.
`seen_at`	integer	Unix seconds when the transaction was first seen.

mempool​

`mempool`