The Right Way to Handle Config Files in Node.js CLI Tools

The Right Way to Handle Config Files in Node.js CLI Tools Every CLI tool eventually needs configuration. Users want defaults they don't have to type every time. Teams want shared settings across projects. CI pipelines want declarative configs checked into version control. But getting config right is surprisingly tricky. Where should the config file live? What format should it use? How do you merge file config with CLI flags? What about environment variables? This article shows you how to build a robust config system that handles all of these cases — using patterns borrowed from ESLint, Prettier, and other battle-tested CLI tools. The Config Hierarchy Good CLI tools resolve configuration from multiple sources, in priority order: CLI flags (highest priority) — --threshold 90 Environment variables — MYTOOL_THRESHOLD=90 Local config file — .mytoolrc.json in the project User config file — ~/.config/mytool/config.json Built-in defaults (lowest priority) Each level overrides the one below it.