An interface with no members serves no purpose. Either the interface extends another interface, in which case the supertype can be used, or it does not extend a supertype in which case it is the equivalent to an empty object. This rule will capture these situations as either unnecessary code or a mistaken empty implementation.

Invalid:

interface Foo {}
interface Foo extends Bar {}

Valid:

interface Foo {
  name: string;
}

interface Bar {
  age: number;
}

// Using an empty interface as a union type is allowed
interface Baz extends Foo, Bar {}