Why transaction value can be zero during a token swap

A transaction's native value field measures the native currency attached to that call. It does not total every token movement caused by the call. An ERC-20 swap can therefore show zero native value while exchanging nonzero token amounts.

Two accounting systems

Ethereum's transaction documentation separates native value from input data. The ERC-20 standard defines token balances and transfer operations inside token contracts.

Imagine a hypothetical transaction calling a router with zero native value. Its input data asks the router to exchange 100 A for B. With the required authorization, execution transfers A through the token contract and delivers B through another token contract. Those balance changes do not need to appear as native value on the outer transaction.

Zero value does not mean zero consequence

The same distinction applies to approvals. A zero-value call can change which contract may move a token. Looking only at native value would miss that state change entirely.

Network charges are also separate from the attached value. A transaction with zero attached native currency can still consume gas, paid according to the chain's transaction rules. Conversely, a native-asset swap may attach value because the asset being exchanged is the network's native currency.

Read the record in layers

1. Identify the outer call's target, native value and decoded action.
2. Inspect the input and output token transfers associated with successful execution.
3. Check the actual account balance change for the asset of interest.
4. Keep network charges separate from swap principal.

A token transfer list is useful but still requires interpretation: routers may include intermediate transfers, wrapping operations or refunds. Summing every displayed movement can double-count tokens that pass through several contracts.

The correct question is not “Why does this transaction say zero?” but “Which field am I reading, and which asset does that field describe?” Once the units and accounting layer are explicit, the apparent contradiction disappears.