How to Configure AGENTS.md and Cursor Rules for Next.js App Router Projects

Coding agents lack awareness of a project's conventions by default, which can lead to architectural mistakes like misplaced data fetching or exposed environment variables in Next.js codebases. A practical solution involves maintaining a root AGENTS.md file that documents the project's actual architecture, including router choices, component patterns, and secret management rules. A lean CLAUDE.md can then point Claude Code to that baseline, avoiding duplication that tends to drift out of sync over time. Cursor project rules stored as .mdc files allow the same guidance to surface contextually, scoped to relevant file paths using globs rather than applied globally. The setup requires no runtime dependencies and is intended as a starting baseline, not a replacement for CI pipelines, code review, or security practices.