Limits

What peakmark does not see.

gzip and brotli sizes come from peakmark’s own encoders. Another encoder at the same settings lands within a fraction of a percent, not on the same byte.
Memory is counted in pages of 64 KiB. Growth smaller than a page per run shows only once it crosses a page; raise repeat to see it.
A memory the module imports instead of exporting is not seen.
Scenarios run in Node, not in a browser: DOM and layout are not part of the measurement.
peakmark measures finished artifacts and does not build them.