JavaScript bundle analyzer

Sizes are UTF-16 unit counts: exact for ASCII code, a close proxy elsewhere, since source map columns are UTF-16 units by the v3 spec. With the bundle supplied, every generated unit is charged to the segment that maps it, down to line ends and breaks, so the split is exact and whatever is left lands in the unmapped bucket. Map-only runs read sourcesContent lengths, or mapped-segment counts when the map carries no contents, and those are proportions, not shipped bytes. The gzip figure uses default settings; servers sending Brotli usually land 15 to 20 percent below it. The tool reads nothing from your filesystem beyond the file you pick, uploads nothing, and does not simulate tree-shaking or minification: it reports the bytes as they shipped.