# Use Reentrancy Guards Reentrancy is generally not expected behavior in most smart contracts, with the exception of callback systems like those used in Uniswap. As a best practice, this behavior should be restricted unless explicitly necessary. In practice, all state-changing functions that include external calls should be protected by a reentrancy guard by default, and any removal of this protection should only occur after a thorough assessment of its impact. If gas optimization is a concern, consider using a reentrancy guard library that leverages [transient storage](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/ReentrancyGuardTransient.sol). Be aware that some EVM chains do not support transient storage. For details on opcode support across different chains, refer to [evmdiff.com](https://www.evmdiff.com/features?feature=opcodes). --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.optimumsec.xyz/coding/reentrancy-guards.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.