starknet

StarkNet contracts are written in Cairo, not Solidity. Create a project with Scarb, define a #[starknet::contract] module with #[storage], a #[constructor], and interface implementations, then compile with scarb build to produce Sierra output.

Deployment is 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. Multiple contracts can share one declared class hash.

No, StarkNet is not EVM-compatible. It uses the Cairo language, felt252 as the native type, sn_keccak function selectors, and Pedersen-hash-based storage. ETH exists as an ERC-20 token, and every account is a smart contract rather than an EOA.

Use Starknet Foundry's snforge: declare the contract by module name in a #[cfg(test)] module, deploy it with constructor calldata, and call functions through dispatchers. Cheatcodes like start_cheat_caller_address simulate different callers, and #[should_panic] verifies reverts.

VALIDATION_FAILURE means the account contract's __validate__ entrypoint rejected the transaction, usually due to an incorrect signature or wrong private key for the account. Verify the key matches the account's public key and that the account is deployed on the correct network.

An L1 Solidity contract calls sendMessageToL2 on the StarkNet Core contract with the target L2 address, function selector, and payload. The sequencer then invokes the matching #[l1_handler] function on the L2 contract, which should validate the from_address against the authorized L1 sender.