code-modernization

Anthropic's guided modernization for legacy codebases, with an optional live progress pane beside the transcript built as a mod.

A large plugin by Anthropic for modernizing legacy code. Start with /modernize: it assesses the codebase, maps it, mines the business rules from the code and writes a plan you approve, then upgrades, rewrites or rebuilds it, with proof that the new code behaves like the old.

The mod part is the live progress pane: a pane beside the transcript with the map of your code, how far each part has got, each module's proof verdict and what to run next. Its commands are /modernize-panel to show or hide it, /modernize-review-pane to review flagged business rules one card at a time, and /modernize-sign to fill in the plan's approval block. The rest of the plugin works without the pane.

Good to know

The pane is early access. The README says to start Claude Code with CLAUDE_CODE_ENABLE_FUNCTION_HOOKS=1; without it the pane stays off and the rest works as usual.
The plugin sends usage counts, whole numbers only, through Claude Code's own telemetry: never code, names, paths or prompts. Turn it off with the plugin's Usage counts option, CODE_MODERNIZATION_TELEMETRY=0 or Claude Code's DISABLE_TELEMETRY=1. Its README lists every number it sends.
Its classic hooks run a shell script and Python, so Windows needs Git Bash.

Listed in the official Claude plugin directory, which is where you install it from.