AI Agents and Persistent Context: What design.md Teaches Us
A GitHub repository called design.md has been trending recently, accumulating over 1,400 stars. The concept is straightforward: provide AI agents with a persistent design document they can reference throughout their work. This approach addresses a practical challenge in agent development that many teams encounter. The Context Challenge When working on complex tasks, AI agents need to understand the broader picture. What's the architecture? What constraints exist? What approaches have been tried before? Typically, agents get context from: Current conversation (limited window) Code comments (often outdated) Documentation (if it exists) The issue is that this context is fragmented and temporary. When conversation moves forward, earlier context disappears. When documentation is outdated, agents make incorrect assumptions. A design.md provides a single source of truth that persists across sessions. What Belongs in design.md An effective design.md answers these questions: What are we building? Beyond feature lists, document the core purpose. Why does this project exist? What problem does it solve? What are the key architectural decisions? Document major choices and their rationale: "PostgreSQL was chosen over MongoDB because ACID guarantees are required for financial transactions" "Microservices architecture was adopted because components have different scaling requirements" What constraints exist? Technical constraints (performance requirements, browser support), business constraints (budget, timeline), and regulatory constraints (GDPR, HIPAA). What has been tried before? Document failed approaches to prevent agents from suggesting rejected solutions. What are the current challenges? Known issues, technical debt, areas needing improvement help agents prioritize work. How Agents Use design.md When starting a task, agents can: Read design.md to understand context Make decisions aligned with documented architecture Avoid solutions violating constraints Reference design.md i