The is-builtin-module package reliably determines if a given string represents a built-in Node.js module. Crucially, it accounts for the "node:" protocol used for disambiguation, returning true for 'node:fs' but not 'fs'. It's essential for tooling that needs to distinguish between core modules and user-installed dependencies. This prevents accidental attempts to install or handle native modules as external packages, ensuring correct behavior in module resolution and dependency management pipelines.