All pending transactions — `mempool`

Subscribe to the mempool channel to receive an event for every pending (unconfirmed) transaction as 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 feature

This stream is an optional feature and may not be available on every network. Subscribing where pending tracking is unavailable succeeds, but no events arrive.

`mempool`

{
  "type": "mempool",
  "data": {
    "txid": "4a5e1e...",
    "seen_at": 1740391012,
    "vsize": 141,
    "fee": "1410",
    "feerate": 10.0,
    "vin": [
      { "prev_txid": "1f3c2b...", "prev_n": 2, "prev_amount": "70000" }
    ],
    "vout": [
      { "n": 0, "amount": "50000" },
      { "n": 1, "amount": "18590" }
    ]
  }
}

Field	Type	Description
`txid`	string	Transaction id.
`seen_at`	integer	Unix seconds when the transaction was first seen.
`vsize`	integer	Virtual size of the transaction, in vbytes.
`fee`	string \| `null`	Fee in the smallest unit (satoshis), as a string; `null` when an input could not be resolved.
`feerate`	number \| `null`	Fee rate in satoshis per vbyte; `null` when the fee is unknown.
`vin`	array	Inputs (see below).
`vout`	array	Outputs (see below).

Input (each item of vin)

Field	Type	Description
`prev_txid`	string	Transaction of the output being spent.
`prev_n`	integer	Output index being spent.
`prev_amount`	string	Value of the spent output, in the smallest unit (satoshis), as a string. Present only when it could be resolved.

Output (each item of vout)

Field	Type	Description
`n`	integer	Output index within the transaction.
`amount`	string	Value in the smallest unit (satoshis), as a string.

mempool​

`mempool`