SonarLint is a tool that helps developers catch common pitfalls and errors in their React code, such as dead code, which can slow down the development process. It uses rules like "react/no-unused-class-component-methods" to detect unused methods in React components and reports them instantly. Additionally, SonarLint can also detect undead code, which refers to component methods that appear to be dead code but are actually being used dynamically with a property accessor or passed as props to another component. By using SonarLint, developers can prevent issues before they happen and improve the overall quality of their code. The tool is free and open-source, and it provides explanations for the rules in the rule description.