Sway provides multiple layers of safety. For one, we provide canonical tooling and "one right way" to do things. This results in less ambiguity and more correct/helpful tools. This tooling ships a debugger, gas profiler, testing framework, SDK, formatter, and more. These tools ensure the programmer has nothing between them and the algorithm they are trying to implement. Safety comes from the foundation of a comfortable and ergonomic environment.
In addition, Sway has implemented static analysis checks like a Checks, Effects, Interactions checker, state and storage purity checking, immutable-by-default semantics, and other static compile-time audits to promote safety.