Vim What?Commands.
.

The . command in Vim

Command

repeat last

Repeat the last change. One of the most powerful keys in Vim — combine with motions and n to apply changes across a file efficiently.
Examples
Related plugin

tpope/vim-repeat — Makes . work correctly with plugin commands (vim-surround, vim-commentary, etc.) instead of only built-in changes.

Reference

Official Vim help for .

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Related commands