Vercel publishes design.md at a public URL and measured 57% fewer mechanical failures.

Vercel's agents load vercel.com/design.md alongside a bounded stylesheet at vercel.com/geist/vercel-brand.css, so they pick from existing CSS classes and tokens (Vercel). Generating three scenarios twice, pages built with design.md had 39 mechanical failures against 91 without. The technique carrying the load is writing observable decisions like "evidence tables use full available width" rather than vague directives, plus a list of named anti-patterns. Vercel is upfront that only six pages were tested and the checks only catch previously-documented failures. Still the most concrete design-system-for-agents artifact I have seen.