**tab** is a tiny library that lets JavaScript CLI authors ship shell‑completion scripts for their tools with a few lines of code, and it also provides ready‑made completions for the major package managers (npm, pnpm, yarn, bun). It works across the common shells (zsh, bash, fish, PowerShell) and offers adapters for popular frameworks such as CAC, citty and commander, making it useful for both CLI library maintainers and end‑users who want instant tab‑completion in their terminals.