IconVault's Import Maps Playground shows you exactly how the browser turns a bare specifier like "lodash" into a URL. Write your import map JSON, write module code that imports from it, then press resolve to see which exact key, prefix key or scope matched each import, and the final resolved URL.

It handles the tricky parts: longest-prefix matching, scoped imports that remap a package for part of your app, and the unmapped specifier error the browser would throw. Everything is free and runs fully in your browser, making it the fastest way to debug an import map before shipping it.