Vercel's design.md is a working example of what might be called context engineering for design intent — a markdown file that encodes brand voice, visual rules, and component preferences in a form agents can consume directly. Rather than relying on an agent to infer brand appropriateness from examples or system prompts alone, design.md acts as a durable, version-controlled specification that travels with the codebase and shapes every page-generation task.
The core infrastructure insight is that brand judgment — normally tacit, held by senior designers and expressed through review cycles — can be made explicit enough to be agent-consumable without losing its nuance. This is a meaningful shift: instead of a human approving every output for on-brand compliance, the compliance criteria are injected at dispatch time as structured context. The agent is constrained before it acts, not corrected after.
For UX practitioners, this raises a design question worth sitting with: what other tacit human judgment can be encoded this way, and at what point does the spec become too brittle to reflect how the brand actually evolves? design.md also implies a new design artifact category — not a style guide written for humans, not a token system written for tools, but something in between, authored for agents and maintained like code.