Enable nullable reference types in a C# project and systematically resolve all warnings. Use when adopting NRTs in existing codebases, performing file-by-file or project-wide nullable migration, fixing CS8602/CS8618/CS86xx warnings, annotating APIs for nullability, cleaning up null-forgiving operators, or upgrading dependencies with new nullable annotations.
Install
npx skills add microsoft/upgrade-agent-plugins --skill migrating-csharp-nullable-referencesnpx skills add microsoft/upgrade-agent-plugins --skill migrating-csharp-nullable-references -a claude-code -gnpx skills add microsoft/upgrade-agent-plugins --skill migrating-csharp-nullable-references -a codex -ggemini skills install https://github.com/microsoft/upgrade-agent-plugins.git --path plugins/upgrade-agent/upgrade/dotnet/skills/lazy/common/migrating-csharp-nullable-referencesgh skill install microsoft/upgrade-agent-plugins migrating-csharp-nullable-referencesgit clone --depth 1 https://github.com/microsoft/upgrade-agent-plugins /tmp/microsoft__upgrade-agent-plugins
mkdir -p ~/.claude/skills ~/.agents/skills
cp -R /tmp/microsoft__upgrade-agent-plugins/plugins/upgrade-agent/upgrade/dotnet/skills/lazy/common/migrating-csharp-nullable-references ~/.claude/skills/migrating-csharp-nullable-references # Claude Code
cp -R /tmp/microsoft__upgrade-agent-plugins/plugins/upgrade-agent/upgrade/dotnet/skills/lazy/common/migrating-csharp-nullable-references ~/.agents/skills/migrating-csharp-nullable-references # Codex, Cursor, Gemini CLI, Copilot, OpenCode