Why I Use an INSTRUCTIONS.md File
The Prime Directive for AI Working On My Codebase
In every AI-assisted codebase I work on, one file quietly shapes everything: INSTRUCTIONS.md.
It’s not a style guide. It’s not a checklist. It’s a contract between me and the AI—a way to ensure that tools like Claude, GPT, and Junie can work inside my system, not just next to it.
Here’s what it does, and why it matters:
🧠 It Encodes My Engineering Philosophy
The file outlines how I want code written—clarity over cleverness, best practices over shortcuts, simplicity over abstraction.
✅ Use community-validated libraries
✅ Prefer minimal working implementations
✅ Validate assumptions before changing behavior
This prevents AI from “hallucinating architecture” or introducing trendy tools I didn’t ask for.
🧪 It Enforces My Standards Without Micromanaging
Instead of repeating the same dev principles in every conversation, I point the AI to this file.
All core logic must have tests
Every function needs JSDoc
All API calls must handle edge cases
It turns vague prompts into production-worthy pull requests.
📝 It Makes Documentation a First-Class Citizen
AI can be a great co-writer, but only if it knows what needs to be written.
INSTRUCTIONS.md defines roles for every doc file:
README.md= usage + architecturePROJECT.md= decisions and stack rationalePROGRESS.md= task logs and blockersABOUT.md= optional narrative layer
This gives structure to what’s usually an afterthought.
🔄 It Supports Automation and CI from Day One
It lays out pre-commit hooks, test expectations, and even how to rotate logs automatically.
No “we’ll add that later.” It’s there from the start.
🧭 Why This Works
AI tools are evolving fast. But they still benefit from context, constraints, and culture. INSTRUCTIONS.md gives them all three. It helps me work faster, make fewer decisions twice, and trust that the machine knows how I think.
It’s not a rulebook. It’s a collaborative operating system for agentic coding.
Want a template to start with? I’ll share mine. Just reply or check [the GitHub link coming soon].
Let me know if you use something similar—or if you want help setting one up.