yarn‑or‑npm is a tiny Node utility that detects whether a project is using Yarn or npm (based on lockfiles, installed binaries, etc.) and then runs commands with the appropriate client. It provides a simple programmatic API (`yarnOrNpm()`, `spawn`, `hasYarn`, `hasNpm`) as well as a CLI (`yarn-or-npm` / `yon`) so developers can write scripts that work transparently with either package manager. It’s aimed at JavaScript/Node developers who want their build or publish scripts to be agnostic to Yarn or npm.