Skills, agents, and hooks you add to .claude/ are powerful — but they are locked to one project. Every time you start a new repo you copy the same files, maintain them in multiple places, and drift out of sync. Claude Code plugins solve this: a plugin is a shareable, versioned package that carries all your customisations and can be installed in any project with one command. This post covers what plugins are, when to use them, and how to build a real one from scratch — a DevOps helper that ships a deployment skill, a pre-deploy safety hook, and an MCP server connection to your Kubernetes cluster.