Smart Contract Invariant

A smart contract invariant is a property or condition of a system that must always remain true throughout the execution of a contract. In financial protocols, invariants are used to guarantee core economic properties, such as the total supply of tokens or the solvency of a pool.

For instance, in a liquidity pool, the product of the reserves of two assets must remain constant after a trade. Developers code these invariants to prevent unauthorized state changes or economic exploits.

If a transaction attempts to violate an invariant, the contract execution reverts, preventing the system from entering an invalid state. These checks are fundamental to the security of decentralized finance applications.

They serve as a mathematical defense against bugs and malicious actors attempting to bypass protocol rules.