Mono is 400 icons drawn over a winter of evenings: one weight, one grid, one opinion. No duotone variants, no fill versions, no 16-and-20-and-24 sizes. The constraint is the product.
The grid rules
Every glyph lives on a 24-pixel grid with a 1.5px stroke, 2px corner radius, and a two-pixel safety margin. Curves snap to quarter-pixel increments so nothing shimmers at 1x. Optical corrections are allowed but documented — every icon that breaks the grid links to a note explaining why, which keeps the exceptions honest and the pull requests civil.
Process
I drew the first eighty icons before writing any tooling, because rules invented before the work always turn out wrong. Then the rules got encoded: a Node pipeline lints every SVG for stroke width, grid alignment, path count, and viewBox, and the CI check fails on any icon the linter can't verify. Contributions went from gently wrong to mechanically consistent overnight.
$ mono lint icons/
✓ 400 icons checked
✗ arrow-up-right: stroke 1.25 (expected 1.5)
✗ calendar: unaligned point at 11.3,7
2 problems, 0.4sWhere it went
Mono ships as raw SVGs, a React package, and a Figma library that stays in lockstep via the same pipeline. It gets about 60,000 npm downloads a month, and the Figma community file has been duplicated 9,000 times. My favorite sighting was in the seatback UI of an airline I won't name — proof that icons, like water, flow everywhere.