Safely change and test untested codebases using Feathers' "Working Effectively with Legacy Code". Use when the user mentions "legacy code", "no tests", "untested codebase", "how do I test this", "seams", "characterization tests", "golden master", "sprout method", "afraid to change this code", "monster method", "dependency breaking", or "inherited a messy codebase".
Install
npx skills add wondelai/skills --skill working-with-legacy-codenpx skills add wondelai/skills --skill working-with-legacy-code -a claude-code -gnpx skills add wondelai/skills --skill working-with-legacy-code -a codex -ggemini skills install https://github.com/wondelai/skills.git --path working-with-legacy-codegh skill install wondelai/skills working-with-legacy-codegit clone --depth 1 https://github.com/wondelai/skills /tmp/wondelai__skills
mkdir -p ~/.claude/skills ~/.agents/skills
cp -R /tmp/wondelai__skills/working-with-legacy-code ~/.claude/skills/working-with-legacy-code # Claude Code
cp -R /tmp/wondelai__skills/working-with-legacy-code ~/.agents/skills/working-with-legacy-code # Codex, Cursor, Gemini CLI, Copilot, OpenCode