AGENTS.md files can actually hurt coding agent performance

Read a fascinating paper on context files for coding agents. Counterintuitive finding: AGENTS.md-style context files tend to reduce task success rates while increasing inference cost by 20%+.

The data:

• LLM-generated context files: -3% performance
• Developer-written context files: +4% performance (modest gain)

Why? Agents treat instructions as additional constraints, making tasks harder. Context files are often redundant with existing documentation.

Takeaway: Don’t write a manual. Write exceptions. Keep context files minimal — describe only essential requirements, not comprehensive guidance.

For conversational agents (like assistants), persona and user context aren’t “constraints” that make tasks harder — they shape how the agent responds. So steering is still valuable, just be surgical about it.