Locktime and sequence

Most transactions can be mined the moment they’re broadcast. Two small fields let a transaction say otherwise: “not before block such-and-such”, or “not until this coin is so many blocks old”.

The locktime sits at the very end of the transaction and applies to the whole thing. The sequence sits in each input and has grown three jobs over Bitcoin’s history. Pearl inherited both unchanged, switched on from block 1. Its wallet, though, leaves them at their “off” values.

Try it

The OP_RETURN example signals replace-by-fee. Find its sequence field.

What is the locktime?

Size

4 bytes

Type

Unsigned integer

Format

Little-endian

Range

0 to 4,294,967,295

The last four bytes of every transaction. The value is read three ways:

There’s an escape hatch: if every input’s sequence is ffffffff, the locktime is ignored altogether.

Here are the locktime bytes of a real payment, 00000000:

A typical payment: 1 input, 2 outputs 205 bytes Copy

01000000 00 01 01 5939557091bae792be66f26cbd83fc78f16a690a854109e8a1d115e253812133 ab020000 00 ffffffff 02 b0359f1100000000 22 5120d7ab02c96a342bdddb5d07b9f3ebd6c04e077ff41418110b9a1e5997439416b2 00c2eb0b00000000 22 512062e9da3682aab288392cf7218bafc36287288abb3ce200c5d1a50aa234073b2b 01 40 4686c7014749649b25555874c7772ecb7a44e85454893ed5888db11ebcdc82a22d74ce1a1671d02810f5ba1dca3277409e95a653ba9644099f7da26be7a86ba2 00000000

Hover or focus the bytes to name each field Version bytes 0–3 1 Marker bytes 4 0x00 Flag bytes 5 0x01 Input count bytes 6 1 Previous txid bytes 7–38 33218153e215d1a1e80941850a696af178fc83bd6cf266be92e7ba9170553959 Output index bytes 39–42 683 scriptSig length bytes 43 0 Sequence bytes 44–47 0xffffffff Output count bytes 48 2 Amount bytes 49–56 295,646,640 grains (2.95646640 PRL) Script length bytes 57 34 Locking script bytes 58–91 prl1p674s9jt2xs4amk6aq7ul867kcp8qwll5zsvpzzu6revewsu5z6eqv9d5z4 Amount bytes 92–99 200,000,000 grains (2.00000000 PRL) Script length bytes 100 34 Locking script bytes 101–134 prl1pvt5a5d5z42egswfv7uscht7rv2rj3z4m8n3qp3w35592ydq88v4seuhn70 Witness items bytes 135 1 Schnorr signature length bytes 136 64 Schnorr signature bytes 137–200 4686c7014749649b25555874c7772ecb7a44e85454893ed5888db11ebcdc82a22d74ce1a1671d02810f5ba1dca3277409e95a653ba9644099f7da26be7a86ba2 Locktime bytes 201–204 0

Field	Bytes	Value
Version version	4 @0	1 int32 little-endian. Pearl wallets and pearld coinbases use version 1; relay policy accepts 1-2.
Marker marker	1 @4	0x00 Segwit marker (BIP-144): says witness data follows the outputs.
Flag flag	1 @5	0x01 Witness flag; 0x01 is the only value Pearl accepts.
Input count vin.length	1 @6	1 CompactSize number of inputs.
Previous txid vin[0].txid	32 @7	33218153e215d1a1e80941850a696af178fc83bd6cf266be92e7ba9170553959 The transaction being spent, stored byte-reversed (internal order); shown here in normal display order.
Output index vin[0].vout	4 @39	683 Which output of that transaction is spent (uint32 LE).
scriptSig length vin[0].scriptSig.length	1 @43	0 Always 0 for non-coinbase inputs in Pearl: every spend uses the witness instead.
Sequence vin[0].sequence	4 @44	0xffffffff Final (0xffffffff): no RBF signal, no relative locktime, and locktime is ignored for this input. Pearl wallets use this.
Output count vout.length	1 @48	2 CompactSize number of outputs.
Amount vout[0].value	8 @49	295,646,640 grains (2.95646640 PRL) int64 little-endian, in grains (1 PRL = 100,000,000 grains).
Script length vout[0].scriptPubKey.length	1 @57	34 CompactSize length of the locking script.
Locking script vout[0].scriptPubKey	34 @58	prl1p674s9jt2xs4amk6aq7ul867kcp8qwll5zsvpzzu6revewsu5z6eqv9d5z4 OP_1 OP_PUSHBYTES_32 <output key Q>: a Taproot output.
Amount vout[1].value	8 @92	200,000,000 grains (2.00000000 PRL) int64 little-endian, in grains (1 PRL = 100,000,000 grains).
Script length vout[1].scriptPubKey.length	1 @100	34 CompactSize length of the locking script.
Locking script vout[1].scriptPubKey	34 @101	prl1pvt5a5d5z42egswfv7uscht7rv2rj3z4m8n3qp3w35592ydq88v4seuhn70 OP_1 OP_PUSHBYTES_32 <output key Q>: a Taproot output.
Witness items witness[0].length	1 @135	1 Number of witness stack items for input 0.
Schnorr signature length witness[0][0].length	1 @136	64 CompactSize length of this witness item.
Schnorr signature witness[0][0]	64 @137	4686c7014749649b25555874c7772ecb7a44e85454893ed5888db11ebcdc82a22d74ce1a1671d02810f5ba1dca3277409e95a653ba9644099f7da26be7a86ba2 64-byte BIP-340 signature (R.x ‖ s) with SIGHASH_DEFAULT: a Taproot key-path spend.
Locktime locktime	4 @201	0 0: no time lock.

txid

d919e02a4adfd739ceef31d98803f0ddd24e1b1fa67b0fe572cdec42c1b384c9

Size

205 bytes · 154 vbytes

Block

130,825

Fee

7,915 grains

Which clock do time locks use?

Not the block’s own timestamp, which a miner could fudge. Time locks are compared with the median time past: the median timestamp of the previous 11 blocks (BIP-113).

Pearl adds a twist. Each block’s timestamp must be at least one second after its parent’s, so timestamps only go up, and the median of 11 is simply the 6th most recent. At the 194-second target, that’s roughly five block intervals, about 16 minutes, behind the latest block. (An estimate from the rules, not a measurement.)

What is the sequence number?

Size

4 bytes per input

Type

Unsigned integer

Format

Little-endian

Satoshi meant it for updating unconfirmed transactions. That idea was dropped, and the field was later reused, bit by bit:

A real transaction from block 130,809 uses fdffffff, that is 0xfffffffd: it signals replace-by-fee, and since its top bit is set, it isn’t a relative lock.

Carries an OP_RETURN data output 253 bytes Copy

02000000 00 01 01 45e83fb8acdfc3cbe7a71b17fe2a05a807fc2222100aab42081ad4e40f344ead 02000000 00 fdffffff 03 b881db2f0b000000 22 5120894b4852db6a243fb705236b47da5ccb18c3ba896c5b0838b9d5c2e93a2efcf4 0000000000000000 27 6a2550524c5501be1688fc1b2fc0671d18c396f9daed531579848f1f8cf002d1579ee333d9ae87 87214249d7050000 22 5120a26b47f694abf29858cc7d1eb44319fc31c12f8bd093d042003b27f9ba91731b 01 40 834fa0d9eb91ac59fcf21e911b43eca33608b6b8393c6a304a959cfaeebbb505ff38d095905be416e78c70ae3fe6d018d823d6ff36467f3199bea33f91976c71 00000000

Hover or focus the bytes to name each field Version bytes 0–3 2 Marker bytes 4 0x00 Flag bytes 5 0x01 Input count bytes 6 1 Previous txid bytes 7–38 ad4e340fe4d41a0842ab0a102222fc07a8052afe171ba7e7cbc3dfacb83fe845 Output index bytes 39–42 2 scriptSig length bytes 43 0 Sequence bytes 44–47 0xfffffffd Output count bytes 48 3 Amount bytes 49–56 48,047,555,000 grains (480.47555000 PRL) Script length bytes 57 34 Locking script bytes 58–91 prl1p3995s5kmdgjrldc9yd450kjuevvv8w5fd3dssw9e6hpwjw3wln6qstfvct Amount bytes 92–99 0 grains (0.00000000 PRL) Script length bytes 100 39 Locking script bytes 101–139 OP_RETURN data (unspendable) Amount bytes 140–147 6,422,205,178,247 grains (64222.05178247 PRL) Script length bytes 148 34 Locking script bytes 149–182 prl1p5f450a5540efskxv050tgscelscuztut6zfaqssq8vnlnw53wvdsmw4yvs Witness items bytes 183 1 Schnorr signature length bytes 184 64 Schnorr signature bytes 185–248 834fa0d9eb91ac59fcf21e911b43eca33608b6b8393c6a304a959cfaeebbb505ff38d095905be416e78c70ae3fe6d018d823d6ff36467f3199bea33f91976c71 Locktime bytes 249–252 0

Field	Bytes	Value
Version version	4 @0	2 int32 little-endian. Pearl wallets and pearld coinbases use version 1; relay policy accepts 1-2.
Marker marker	1 @4	0x00 Segwit marker (BIP-144): says witness data follows the outputs.
Flag flag	1 @5	0x01 Witness flag; 0x01 is the only value Pearl accepts.
Input count vin.length	1 @6	1 CompactSize number of inputs.
Previous txid vin[0].txid	32 @7	ad4e340fe4d41a0842ab0a102222fc07a8052afe171ba7e7cbc3dfacb83fe845 The transaction being spent, stored byte-reversed (internal order); shown here in normal display order.
Output index vin[0].vout	4 @39	2 Which output of that transaction is spent (uint32 LE).
scriptSig length vin[0].scriptSig.length	1 @43	0 Always 0 for non-coinbase inputs in Pearl: every spend uses the witness instead.
Sequence vin[0].sequence	4 @44	0xfffffffd signals opt-in replace-by-fee (BIP-125).
Output count vout.length	1 @48	3 CompactSize number of outputs.
Amount vout[0].value	8 @49	48,047,555,000 grains (480.47555000 PRL) int64 little-endian, in grains (1 PRL = 100,000,000 grains).
Script length vout[0].scriptPubKey.length	1 @57	34 CompactSize length of the locking script.
Locking script vout[0].scriptPubKey	34 @58	prl1p3995s5kmdgjrldc9yd450kjuevvv8w5fd3dssw9e6hpwjw3wln6qstfvct OP_1 OP_PUSHBYTES_32 <output key Q>: a Taproot output.
Amount vout[1].value	8 @92	0 grains (0.00000000 PRL) int64 little-endian, in grains (1 PRL = 100,000,000 grains).
Script length vout[1].scriptPubKey.length	1 @100	39 CompactSize length of the locking script.
Locking script vout[1].scriptPubKey	39 @101	OP_RETURN data (unspendable) OP_RETURN data carrier: provably unspendable, never enters the UTXO set.
Amount vout[2].value	8 @140	6,422,205,178,247 grains (64222.05178247 PRL) int64 little-endian, in grains (1 PRL = 100,000,000 grains).
Script length vout[2].scriptPubKey.length	1 @148	34 CompactSize length of the locking script.
Locking script vout[2].scriptPubKey	34 @149	prl1p5f450a5540efskxv050tgscelscuztut6zfaqssq8vnlnw53wvdsmw4yvs OP_1 OP_PUSHBYTES_32 <output key Q>: a Taproot output.
Witness items witness[0].length	1 @183	1 Number of witness stack items for input 0.
Schnorr signature length witness[0][0].length	1 @184	64 CompactSize length of this witness item.
Schnorr signature witness[0][0]	64 @185	834fa0d9eb91ac59fcf21e911b43eca33608b6b8393c6a304a959cfaeebbb505ff38d095905be416e78c70ae3fe6d018d823d6ff36467f3199bea33f91976c71 64-byte BIP-340 signature (R.x ‖ s) with SIGHASH_DEFAULT: a Taproot key-path spend.
Locktime locktime	4 @249	0 0: no time lock.

txid

4ce980a19e940dadd3ecb0ca5c59e05880c252c254ae5f690bfaac7d6c642e0c

Size

253 bytes · 202 vbytes

Block

130,809

Fee

10,200 grains

How does a relative lock work?

A relative lock says “the coin this input spends must be at least N blocks (or N × 512 seconds) old”. It’s written in the sequence number when the transaction’s version is 2 or higher:

Scripts can demand these locks too: OP_CHECKLOCKTIMEVERIFY (BIP-65) and OP_CHECKSEQUENCEVERIFY (BIP-112) work in Pearl’s tapscript, as in Bitcoin. All of these rules are on from the first block; Pearl never had a soft-fork activation for them.

What is replace-by-fee on Pearl?

Replace-by-fee lets you swap an unconfirmed transaction for a new version that pays a higher fee. On Pearl it’s opt-in only, as in Bitcoin’s BIP-125:

• A transaction is replaceable if any of its inputs has a sequence of fffffffd or less, or if an unconfirmed ancestor signals.
• The replacement must pay a strictly higher fee rate than each transaction it replaces, and an absolute fee at least their total plus the minimum relay fee for its own size.
• It may evict at most 100 transactions, may not add new unconfirmed inputs, and may not spend the outputs it replaces.
• A node started with -rejectreplacement refuses all replacements.

There is no “full RBF” mode, in which any transaction can be replaced whether it signals or not.

What does Pearl’s wallet write?

Bitcoin Core’s wallet does differently: version 2, and a locktime set to the current height to discourage miners from rewriting recent blocks (“anti-fee-sniping”). Pearl’s wallet does neither.