Static type checkers are tools that analyze code without executing it to ensure that variables are used consistently according to their defined types. They help catch errors early in the development process by verifying that operations on variables are appropriate for their data types, such as ensuring that a string is not mistakenly used as a number. These checkers are commonly used in programming languages like Java, C#, and TypeScript, where type definitions are explicitly declared. By identifying type-related issues before runtime, static type checkers improve code quality and reduce the likelihood of bugs, making software development more efficient.