vim-which-key is a Vim/Neovim plugin that provides an interactive keybinding guide. When a leader key is pressed, it intercepts subsequent keystrokes and displays available mappings in a popup or split window. The plugin dynamically parses native Vim mappings for the given prefix and merges them with user-defined description dictionaries to show meaningful labels and group names. It supports both Vim's popup API and Neovim's floating windows, offering a modern, non-intrusive UI. The architecture is modular: mapping parsing, layout rendering, window management, and key input handling are separated into distinct autoload modules. The code demonstrates solid Vimscript engineering, with careful handling of edge cases like timeout, exit codes, special keys, and fallback to native mappings.