The photograph

The picture behind every page on this site is Corylus avellana RF.jpg by Robert Flogaus-Faust, used under CC BY 4.0 and reached through Wikimedia Commons: https://commons.wikimedia.org/wiki/File:Corylus_avellana_RF.jpg.

It is a hazel in flower. Hazel is the wood a tally stick was cut from, and the catkins hang in matched pairs, which is this site's whole idea photographed rather than drawn. What ships is cropped, softened and toned — never the original file — and the tone is a measurement rather than a taste: Cropped by tools/crop.mjs through Chrome's canvas (2% off the top; there is no image library on this machine and sips crops only about the centre), then softened and toned by tools/make-ground.mjs: blur 5px, saturate 1.3, brightness 1.22, and a highlight knee at 0.72 keeping 40% of the range above it. The knee is there for a measured reason: the catkins ran to rgb(252,233,105), and 52%-white glass over that cleared it by only 1.19:1 — under the 1.25:1 bar every card on this site has to hold. Compressing the highlights lowered the ceiling to 1.37:1 without touching the midtones. The original file is never served.

Nine other photographs were downloaded and measured the same way before this one was chosen; their provenance is recorded in data/photo-candidates.json and the choice, with its reason, in data/photo.json.

The typefaces

  • Newsreader by Production Type, for headings — SIL Open Font License 1.1.
  • Public Sans by the USWDS, for everything else — SIL Open Font License 1.1.
  • JetBrains Mono by JetBrains, for addresses and hashes — SIL Open Font License 1.1.

Served from Google Fonts. The logo files in brand/ embed the few letters they use, so they render the same where the fonts are not installed.

The contracts

Foil deploys nothing. It builds calls to contracts other people wrote and deployed:

Seaport 1.6
0x0000000000000068F116a894984e2DB1123eB395 — the exchange that settles every offer. Written by OpenSea, MIT licensed, deployed here by somebody else before Foil existed.
Uniswap v3 and v4
read only, for the comparison: the quoters, the v3 factory and the v4 state view. Nothing is ever swapped through them by this site.
Multicall3
0xcA11bde05977b3631167028862bE2a173976CA11 — for reading many things at one block.
The stocks and the dollar
tokenized shares issued on Robinhood Chain, and Global Dollar (USDG) issued by Paxos. Neither is ours, and listing one is not an endorsement of it.

The code

  • ethers.js v6 (MIT) — signing, encoding and decoding, in the page and in the tools.
  • Hardhat (MIT) — the local fork every test runs against.
  • solc 0.8.26 (GPL-3.0) — compiles the property harness, which is never deployed.
  • The swap arithmetic in js/sim.js follows Uniswap's own (GPL/BUSL as published by Uniswap Labs) and is checked against their deployed quoters on every run.