linter
/ LINT-er /
A linter is a tool that reads your code and quietly flags likely mistakes and messy style — before you ever run the program. It's the friendly proofreader looking over your shoulder, underlining the bug you were about to ship.
It catches things like an unused variable, a forgotten semicolon, a typo'd name, or inconsistent indentation. Some you must fix; many are just nudges toward tidier, more consistent code your teammates will thank you for.
The name comes from 'lint' — the fuzz a clothes dryer traps. A linter picks the little fluff out of your code. Most editors run one as you type, so problems glow red the moment you make them.
$ npx eslint src/ src/app.js 12:7 warning 'count' is assigned a value but never used
The linter spots an unused variable before you run anything.
A linter judges code quality; a 'formatter' (like Prettier) just reshapes the layout.