How much might this package add to your page?
Search for the public npm package and the version you plan to use. The result estimates how much code a build of that package contains and how much remains after gzip compression. Compare versions and packages using the same displayed measure.
Why can your app download a different amount?
Your app may use only one part of a library, share code it already loads or split features into files that download later. A package estimate cannot see those decisions. Use your app’s own build report to see which files contain the code, then check what the browser actually requests on the page you care about.
What should you enter and save?
The public lookup is available without an installation or account. Enter only a public package name and version. The site offers a beta package-list scan, but a single lookup is enough here. Keep a private note of the package, version and size measure. A missing result can mean a dependency or build error, so leave it unknown.
How would you compare two libraries before choosing?
Imagine two calendar libraries that meet the same needs. Their fictional whole-package gzip estimates are 18 KB and 42 KB. Ask which calendar code is required on the first screen and which can wait until someone opens the calendar. A smaller estimate gives you a candidate to inspect, while your actual app build and browser requests tell you what visitors download.