Glossary
Calldata
The read-only byte array attached to an external call — function selector + ABI-encoded arguments. The cheapest data region in the EVM after stack.
Calldata is the input the caller hands to a transaction or
call. It is read-only from the contract's perspective and lives
outside the EVM's mutable memory and storage. Compared to memory
or storage, reading from calldata is cheap — which is why
calldata is the preferred parameter location for large arrays
in external functions.
Calldata also sits next to a transaction's signature inside the block — making it the natural place rollups posted batched L2 data before EIP-4844 introduced blobs.