Nonce

A nonce is, in general, a "number used once". In blockchain contexts

the word is overloaded. The most common meaning, and the one block

explorers surface for every transaction, is the account nonce on EVM

chains: a counter that tracks how many transactions an externally-owned

account (EOA) has sent.

The account nonce on EVM chains

On ethereum and every EVM-compatible chain

(base, arbitrum one,

optimism, polygon,

bsc, and others), each EOA has a nonce that starts at 0

and increases by one with each successfully included transaction. When a

wallet signs a transaction, it stamps the next sequential nonce into the

transaction data.

The protocol enforces two rules:

• A transaction is only valid if its nonce matches the sender's current

nonce. A future-nonce transaction is queued; a past-nonce transaction is

invalid.

• The nonce is part of the signed payload, so an attacker cannot replay an

old signed transaction (its nonce is already used).

This is why nonces must be sequential: nonce 5 cannot land before

nonce 4. If you broadcast nonce 4 followed by nonce 6, the chain holds

nonce 6 until nonce 5 arrives.

Why explorers show it

Explorers display the nonce on every transaction page and use it to order

an address's outgoing transactions. On an account page, the activity list

under "transactions" effectively scans nonces 0, 1, 2, ... for that

account. If a transaction list shows a gap, something is stuck or pending.

The nonce is also how you "replace" a pending transaction: re-broadcasting

the same nonce with a higher fee tells the network to use the new tx

instead. Wallets call this a "speed up" or "cancel". When tx.taxi routes a

lookup of an EVM address, the destination address page on the configured

explorer is where you can see this ordering.

Other things called "nonce"

Several other values share the name. Block explorers usually disambiguate

by context.

• Proof-of-work nonce: a 32-bit value in a block header that miners

vary while searching for a header hash below the difficulty target.

Visible on bitcoin block pages. Unrelated to account

nonces.

• EIP-712 / signature nonce: an application-level nonce embedded in

signed messages (for example, permit signatures for ERC-20 tokens) so

that a contract can ensure each signature is consumed exactly once.

• Cryptographic nonce: any one-shot random value used in primitives

such as authenticated encryption. Not blockchain-specific.

Common gotchas

• Stuck transactions in the mempool often stem from a

low-fee earlier nonce. Everything after it waits.

• Tooling that pre-signs multiple transactions must ensure the nonces are

sequential and that nothing else broadcasts in between, or the later

ones will conflict.

• Contract accounts have nonces too, but the nonce increments per contract

creation (via CREATE), not per outgoing call, which is why contract

nonces look small even for very active contracts.

• Non-EVM chains do not all use sequential account nonces.

solana uses recent blockhashes to bound replay; UTXO

chains use unspent outputs. The "nonce" concept exists, but it is not

the same counter.