Definition
ABI encoding is a mechanism that transforms human-readable function signatures and structured data into a low-level binary representation defined by an Application Binary Interface. It specifies exactly how arguments, return values, and complex data types are laid out in bytes so that smart contracts and external callers interpret them consistently. By following the ABI rules, different tools, wallets, and applications can interact with the same contract without ambiguity about how data is formatted.
This encoding is central to contract calls, event logs, and data storage formats on many smart contract platforms. It ensures that when a function is invoked, the contract receives its parameters in a predictable order and size, and that returned values are decoded correctly. Without ABI encoding, on-chain and off-chain components would lack a shared language for exchanging structured data with smart contracts.
Context and Usage
ABI encoding is typically defined alongside an ABI specification, which lists the functions, events, and data types exposed by a smart contract. When a transaction targets a contract function, the call data field is constructed using ABI encoding so the contract can identify the function and parse its inputs. The same rules apply when decoding event logs or interpreting data returned from contract execution.
In practice, ABI encoding acts as the bridge between higher-level programming languages and the low-level virtual machine that executes smart contracts. It allows on-chain logic and off-chain applications to share a common, deterministic data format, reducing errors caused by mismatched types or ordering. The term is closely related to the ABI itself, which defines the schema that the encoding mechanism must follow.