Unit 2 · Level 1 · Reading transactions
Transfer or contract call?
Every transaction is one of two species. A simple transfer sends coin to a regular address, with the input data field empty and nothing to compute. A contract call sends instructions to a smart contract: the To address is a contract and the input data carries the command, like 'swap' or 'approve'. Telling them apart is your first reading skill.
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What you get asked
How do you tell a contract call from a simple transfer on an explorer?
Look at the To and the input data. A person's address plus empty data = transfer; a contract plus a payload of instructions = a call.
A plain transfer has an empty ___ field. A contract call fills it with encoded instructions.
That blob of hex in the input data is the message to the contract: which function to run and with what arguments.
Match what you see to what the transaction is
Explorers translate the input data into a Method label when they can, a huge shortcut. 'Approve' and 'swap' will star in the next lessons.
Explorers often decode input data into a readable Method name like 'transfer' or 'swap'. Why is that possible?
When a contract's source code is verified on the explorer, the hex payload maps back to human-readable functions. Unverified contracts stay as raw hex, itself a mild warning sign.
Why does a contract call usually cost more gas than a simple transfer?
A transfer is one bookkeeping entry; a swap might run hundreds of operations across several contracts. Gas is priced per unit of work, so more work, bigger fee. 🐜
The rest of this unit
Transfers, approvals, swaps, mints: learn what each really looks like.