Want to build an extension to Spec Kit? This comprehensive guide walks you through everything you need: a ready-to-drop extension layout, a complete extension.yml manifest, a slash-command file, a lifecycle hook that runs a C# helper, a full C# console app (source + csproj), install scripts, CI to build multi-platform artifacts and package the extension, plus troubleshooting, testing, and security advice.

What you’ll get (artifacts shown in this guide)