Sanitize‑Against is a lightweight TypeScript/JavaScript library for runtime validation and sanitisation of incoming data objects. It lets developers define flexible “patterns”—using primitive type checks, optional fields, default values, and logical combinators (OR, AND, NOT)—and then safely filter request payloads to prevent issues such as prototype‑poisoning or malformed inputs. The package is aimed at backend developers who need a simple, highly‑customisable way to enforce object schemas and type safety on server‑side APIs.