Unused state variable

Severity: Gas ID: unused-state-variables

Flags state variables that are declared but never read or written anywhere in the contract or its descendants.

What it does

Reports each state variable that has no read or write site across the project.

Why is this bad?

Unused state variables waste storage slots, inflate deployment cost, and are a strong signal of dead or stale code that should be removed.

Example

Bad

contract C {
    uint256 unused;       // never read or written
    uint256 public total; // used elsewhere
}

Good

contract C {
    uint256 public total;
}

Notes

This is a Gas-severity lint and is not applied to test or script files.