Pending transactions

onMempoolTransaction() calls you for every pending transaction seen on a network, the moment it appears — the whole mempool, not just one address. To follow the pending transactions of a single address, use onPendingTransaction().

const btc = cg.explore(cg.networks.bitcoin)

btc.onMempoolTransaction(({ txid, vsize, feeRate }) => {
  console.log(`${txid} — ${vsize} vB at ${feeRate ?? '?'} sat/vB`)
})

High volume

Busy networks produce several pending transactions per second. Keep the callback light, and prefer the address-scoped events whenever you only care about a few addresses.

Pending events may be unavailable on some networks

Pending tracking is an optional capability of each network. Subscribing where it is not available succeeds, but no events arrive.

UTXO networks

Field	Type	Description
txid	string	Transaction id
seenAt	number	Unix seconds when the transaction was first seen
vsize	number	Virtual size, in vbytes
fee	Amount | null	Fee paid; null when an input could not be resolved
feeRate	number | null	Fee rate in satoshis per vbyte; null when the fee is unknown
inputs[]	{ prevTxid, prevN, prevAmount? }	The outputs being spent; prevAmount is present when it could be resolved
outputs[]	{ n, amount }	The outputs created

EVM networks

Pending events cover the native coin only — gas is not included, and token transfers are not visible until the transaction is mined.

Field	Type	Description
hash	string	Transaction hash
from	string	Sender
to	string | null	Recipient; null for a contract creation
value	Amount	Native value moved
nonce	number	Sender nonce
input	string	Calldata — "0x" for a plain transfer
gas	bigint	Gas limit
gasPrice	bigint | null	Legacy gas price in wei, when present
maxFeePerGas	bigint | null	EIP-1559 max fee per gas in wei, when present
maxPriorityFeePerGas	bigint | null	EIP-1559 priority fee per gas in wei, when present
type	number | null	Transaction type (0 legacy, 1 EIP-2930, 2 EIP-1559), when reported
chainId	number | null	Chain id, when reported
seenAt	number	Unix seconds when the transaction was first seen

const eth = cg.explore(cg.networks.ethereum)

eth.onMempoolTransaction(({ hash, value, maxFeePerGas }) => {
  if (value.min() >= 100n * 10n ** 18n) {
    console.log('Whale alert:', hash, value.base(), 'ETH', 'max fee', maxFeePerGas, 'wei')
  }
})