klbr web ships two open fonts, vendored so the tool works offline.

  ioskeley/IoskeleyMono-{Regular,Medium,SemiBold}.woff2   Ioskeley Mono (c) Ahatem
      https://github.com/ahatem/IoskeleyMono — SIL Open Font License 1.1 (see ioskeley/OFL.txt)
      subset to latin + punctuation + arrows with fontTools; ~49 kB per weight.

  inter/InterVariable.woff2                               Inter (c) The Inter Project Authors
      https://github.com/rsms/inter — SIL Open Font License 1.1 (see inter/LICENSE-Inter.txt)

Ioskeley Mono carries data and prose; Inter carries chrome labels and buttons.
Both are taken from the reference site's own stack (git.t4t.associates serves InterVariable and
Ioskeley Mono), which is why the pairing is not a coin flip.