What is the borrow checker in Rust?

The borrow checker is Rust's compile-time static analysis component that enforces the ownership and borrowing rules. It tracks the scope and lifetime of every reference and ensures no reference outlives the data it points to (preventing dangling pointers), no mutable reference coexists with any other reference to the same data (preventing data races), and no value is used after it has been moved or dropped. When the borrow checker rejects your code, the compiler produces a detailed error message explaining the violation and often suggests how to fix it. The borrow checker is the mechanism that gives Rust its memory safety guarantees without runtime overhead — all checks happen at compile time.