The interface tells software how to format requests and results.
LET’S PICTURE IT
A form specifies field types and action names. It does not necessarily reveal every rule the office uses to accept or reject the form.
SEE IT FOR YOURSELF
Build a transfer call from typed fieldsStep 1 / 4
The standard transfer interface takes an address and a raw integer amount. This diagram uses address one and amount one hundred.
The standard transfer interface takes an address and a raw integer amount. This diagram uses address one and amount one hundred.Keccak-256 of the canonical signature supplies the first four bytes. The transfer selector is a9059cbb.An address is twenty bytes. Standard ABI encoding adds twelve zero bytes on the left to fill one thirty-two-byte word.The integer one hundred is hex 64, left-padded in word one. Selector plus two words produces sixty-eight bytes of standard calldata.
Animated local teaching model. No wallet, RPC or live blockchain data. Some labels and hashes are abbreviated for readability.
Functions have typed inputs
An ABI can describe function names, parameters, outputs and mutability information. Applications use it to prepare calldata and interpret returned bytes. A human-friendly parameter name is helpful documentation rather than a complete behavior guarantee.
Events and errors have shapes too
ABI entries can describe events and custom errors. This lets software decode topic/data layouts or revert data under an expected interface. Bytes do not authenticate the honesty of the contract that constructed them.
The implementation enforces behavior
An ABI does not prove that a deployed address uses that implementation or that a permission check is correct. A selector is short enough for collisions, so identifying an action solely by four bytes has limits.
Try an interface locally
Our encoder and decoder use the interface you choose or supply. They show a request’s selector and argument words without calling the blockchain. Read the advanced ABI lesson once these interface basics are comfortable.