Vercel Releases 'design.md' Brand Design Guide for AI Agents

Vercel has released the design.md file to help its coding agents create pages while maintaining brand identity. Previously, the design system and guidelines were delivered via the product-design skill within the repository. Now, accessibility has been expanded through a single public URL, enabling agents operating in external tools to generate outputs of the same quality.

Limitations of Simple Prompts and Solutions

Initially, the team attempted to convert the contents of product-design into a single prompt. However, this approach resulted in inconsistent page generation because different models interpreted subjective instructions like 'clean layout' differently. To address this, the file was rewritten from scratch to ensure accurate style reproduction even in environments lacking actual components or example code.

Evaluation-Driven Iterative Development

Vercel fixed seven evaluation prompts based on real-world use cases (such as usage reports, renewal proposals, and benchmark reports) and iteratively tested the impact of changes to design.md on the output. This approach helped ensure that models consistently followed design instructions. It was confirmed that applying design.md generates pages that align with Vercel's brand guidelines, rather than generic SaaS dashboards.