Tiny Online Tools
Where did all these bytes go?
A production bundle is one giant minified file. Knowing it's 340 KB tells you nothing about why — which is the question that actually matters when you're trying to cut it down. This tool answers it directly: load the bundle and its .map file, and every byte gets attributed to the original source module that produced it.
How the attribution works
A source map's mappings say "generated column 4110 came from src/utils/format.js." This tool walks every mapping in the file, in order, and measures the gap to the next one on the same generated line — that gap is the span of generated code credited to that mapping's source. It's the same line-level approximation the well-known source-map-explorer CLI tool uses, and it's honest about being an approximation: two adjacent tokens on the same generated line with nothing mapped between them (stray whitespace, a minifier-inserted character) fall into their own unmapped category rather than being silently folded into whichever source happens to be nearby.
Structural bytes — the newlines between generated lines — get their own category too, for the same reason: they belong to the file's structure, not to any one module.
The reconciliation check
Every run shows a literal readout: X bytes attributed of Y total bytes, plus the unmapped and structural counts, and whether attributed + unmapped + structural equals the file's total length exactly. This isn't a cosmetic detail — it's the guarantee that no byte was silently dropped or double-counted, and you can verify it yourself instead of taking the tool's word for it.
Per-file or per-folder
Switch between a row per original source file, or a rollup by top-level folder — node_modules/lodash sums every file lodash contributed, so you can see "how much did this one dependency actually cost" without scrolling past forty individual files first. Everything is sorted by size, largest first, and the CSV export keeps the same numbers for further analysis.
Privacy
Both files are read and processed entirely in your browser. Nothing is uploaded.