Transaction Sequence
Pronunciation: tran-ZAK-shun SEE-kwuhns
Also known as: Transaction Sequence Number
Definition
A transaction sequence is an ordering or control value associated with a transaction or input. Its meaning varies by protocol. It may refer to an account sequence number used for replay protection, or specifically to Bitcoin input sequence fields used for replacement signaling and relative timelocks. It should not be assumed to equal one universal transaction counter.
Overview
How it works and where it fits
Transaction sequence can describe the order in which transactions from an account are accepted. Networks such as account-based ledgers may use a sequence number with behavior similar to a Transaction Nonce. The next transaction must carry the expected value, preventing replay and coordinating dependent actions. The exact rules for failed, pending, and parallel transactions remain network-specific.
In Bitcoin, each transaction input has a sequence field. Historically associated with transaction replacement, it is also used with locktime and relative timelock rules. Because every input can carry a sequence value, it is not a single sender-account counter. Wallets must construct it according to the intended replaceability and spending conditions.
The term can also appear in APIs as a database order, block-local transaction position, or application-generated sequence. These are not automatically consensus fields. A block index position identifies ordering after inclusion, while an account sequence participates in validity before inclusion. Clear naming prevents one value from being substituted for another.
Automated senders should record the sequence domain, source, and associated transaction. For account sequences, they need concurrency and gap management. For Bitcoin input sequences, they need policy-aware fee replacement and timelock handling. A generic “sequence” column without chain and semantic context is insufficient for safe signing or reconciliation.
Production teams benefit from retaining the exact field, input or account scope, intended locktime or replacement behavior, and associated transaction. The record is especially useful because account sequence numbers and Bitcoin input sequence values solve different problems despite similar names. Safeguards should use protocol-native semantics and prevent generic database ordering from being substituted into signing logic.
Implementations should not interchange it with a generic Transaction Counter without confirming the protocol’s exact semantics.
Related glossary concepts
UTXO Set; Transaction Size; Raw Transaction
Primary reference
Example
An Ethereum account uses a nonce to order outgoing transactions; Bitcoin uses an nSequence field per input that can interact with relative timelocks and replacement policy. A wallet developer who maps both to one generic sequence counter may create invalid or unexpectedly locked transactions.
Comparison
Name the network and field explicitly. In Bitcoin, the input sequence does not count how many payments an account has made. In account-based systems, pending transactions with the same nonce can compete under replacement rules. A database event sequence is yet another concept and should not be substituted into transaction signing.
Key Takeaway
Sequence fields have protocol-specific semantics; Bitcoin nSequence is not an account nonce.
Sources
- Bitcoin Developer Guide: Transactions — Bitcoin.org (2026-08-02)
- Bitcoin Transaction Reference — Bitcoin.org (2026-08-02)
- Ethereum Transactions — Ethereum.org (2026-08-02)