write a custom semgrep rule with the user, add it to guardian in either user or repo scope, and prove it fires by writing a file that should trip it. use when someone wants guardian to catch something it currently misses, asks to write or add a semgrep rule, or wants a project convention enforced on the code claude writes.
Install
npx skills add semgrep/guardian --skill add-and-validate-guardian-developer-semgrep-rulenpx skills add semgrep/guardian --skill add-and-validate-guardian-developer-semgrep-rule -a claude-code -gnpx skills add semgrep/guardian --skill add-and-validate-guardian-developer-semgrep-rule -a codex -ggemini skills install https://github.com/semgrep/guardian.git --path plugin/skills/add-and-validate-guardian-developer-semgrep-rulegh skill install semgrep/guardian add-and-validate-guardian-developer-semgrep-rulegit clone --depth 1 https://github.com/semgrep/guardian /tmp/semgrep__guardian
mkdir -p ~/.claude/skills ~/.agents/skills
cp -R /tmp/semgrep__guardian/plugin/skills/add-and-validate-guardian-developer-semgrep-rule ~/.claude/skills/add-and-validate-guardian-developer-semgrep-rule # Claude Code
cp -R /tmp/semgrep__guardian/plugin/skills/add-and-validate-guardian-developer-semgrep-rule ~/.agents/skills/add-and-validate-guardian-developer-semgrep-rule # Codex, Cursor, Gemini CLI, Copilot, OpenCode