starknet

Write Cairo contracts using the #[starknet::contract] attribute with a #[storage] struct, #[constructor] function, and #[abi(embed_v0)] impl blocks for external functions. Build with Scarb, which compiles Cairo to Sierra bytecode for deployment.

Deploy in two steps: first declare the contract class with starkli declare or sncast declare to get a class hash, then deploy an instance with starkli deploy or sncast deploy passing constructor calldata. Fund your account via the Sepolia faucet first.

felt252 is StarkNet's native field element type that wraps on overflow, while u256 is a struct of two u128 values that panics on overflow. Use u256 for token amounts and financial math, and felt252 for hashes and identifiers.

Yes, every StarkNet account is a smart contract implementing __validate__ and __execute__ entrypoints, so there are no EOAs. Multicall is native because __execute__ receives an array of calls, batching multiple operations in one transaction.

VALIDATION_FAILURE means the account contract's __validate__ function rejected the transaction, usually due to an incorrect signature or wrong private key for the account address. Verify your keypair matches the deployed account and the nonce is current.

Send L1-to-L2 messages by calling sendMessageToL2 on the StarkNet Core contract, which triggers a #[l1_handler] function on the L2 contract. For L2-to-L1, call send_message_to_l1_syscall in Cairo, then consume the message on L1 after the state update is proven.