vcdeps wires Microsoft's vcpkg package manager into mkmf: declare native dependencies in ext/<gem>/vcpkg.json, call Vcdeps.mkmf! from extconf.rb, and vcdeps locates (or bootstraps) vcpkg, installs the ports out of tree with the correct dynamic-CRT triplet, prepends the include/lib paths so they win over Ruby's own opt-dir, and vendors the runtime DLLs with a generated Fiddle-preload shim so the built extension actually loads. It provides a library API (install!/vendor!/baseline!/tool!), the extconf entry point Vcdeps.mkmf!, and a CLI (vcdeps doctor/where/install/vendor/ baseline/bootstrap). Manifest mode only; builds and caches live under %LOCALAPPDATA%\vcdeps, never inside the gem. Windows MSVC (mswin) Ruby only. Pure Ruby — no compiler required to install vcdeps itself.