As engineers move between Claude Code, Cursor, Windsurf, and Aider, maintaining duplicate context rules across proprietary config files creates friction. The developer community in 2026 has converged on AGENTS.md as the universal open standard for project memory.
| Specification | Primary Scope | Supported Agents | How It Is Processed |
|---|---|---|---|
AGENTS.md |
Universal Open Standard | Claude Code (v2.1.277+), Cursor, Codex CLI, Aider, Windsurf, Zed, OpenCode, Jules | Ingested at session initiation as root system instructions. Universal cross-tool format. |
CLAUDE.md |
Tool-Specific (Anthropic) | Claude Code CLI, Claude Desktop | Used for sub-agent tool execution permissions and compact build commands. |
.cursor/rules/*.mdc |
Scoped Directory (Cursor) | Cursor IDE | Triggered dynamically via glob patterns (*.ts, *.py) only when relevant files are edited. |
SKILL.md |
Task-Triggered Plugin | Antigravity, OpenCode | Procedural instructions loaded on-demand when specific user intents fire. |
⚠️ Empirical Finding: Pasting full directory trees into root instruction files increases token spend by 20%+ and degrades agent reasoning by 18%.
Modern coding agents already construct Tree-sitter AST maps automatically. Your context files should strictly contain non-inferable build commands, negative constraints (what NOT to do), and commit standards.
# AGENTS.md — Universal Agent Context Specification
## 1. Project Overview & Architecture
- Stack: TypeScript / Node.js (or Python 3.12 / FastAPI)
- Structure: Modular services under `src/`, test suites under `tests/`.
## 2. Essential Commands (Non-Inferable)
- Build: `npm run build`
- Fast Test Loop: `npm test -- --bail`
- Lint & Format: `npm run lint`
## 3. Negative Constraints (What NOT to Do)
- NEVER commit secrets, API keys, or `.env` files.
- NEVER delete or overwrite existing docstrings or test suites without explicit instructions.
- DO NOT use wildcard imports (`from module import *`).
- DO NOT add external dependencies for tasks solvable with standard libraries.
## 4. Code Style & Typing Standards
- All code must pass strict type checking without warnings (`strict: true`).
- Keep functions modular and under 50 lines. Keep files under 300 lines.
- Commits must adhere to Conventional Commits: `feat:`, `fix:`, `refactor:`, `test:`, `docs:`.