Proposal: Add Support for Agent Rules Standard with AGENTS.md for Cross-Agent Interoperability

[sgryphon]

Problem Statement

The AI coding agent ecosystem is increasingly fragmented, with each tool requiring its own configuration files for natural language guidelines—such as YAML-based Custom Modes for defining agent behavior in tasks like code generation or refactoring. This leads to duplication when developers use multiple agents, increasing maintenance efforts, version control complexity, and the risk of inconsistencies in rules like coding styles, security practices, or workflows.

Proposed Feature

To address this, I suggest adding support for the Agent Rules standard, a minimalist community specification that uses a single AGENTS.md file in the project root to provide shared natural language instructions. This would allow users to define rules once and reuse them across compatible agents, integrating seamlessly alongside existing Custom Modes without replacement.

Kilo already supports fallback to cline and roo rules, so fall back to a standard AGENTS.md should be an easy add for global support. https://kilocode.ai/docs/advanced-usage/custom-rules

For the full specification, examples, and a list of supporting tools, please refer to https://agent-rules.org/.

Benefits

• Standardized Approach: By adopting a common format inspired by successful standards like EditorConfig and Semantic Versioning, it reduces redundancy and promotes best practices in natural language configs (Markdown or plain text, no mandatory structure).
• Interoperability: Rules in AGENTS.md can be shared with other agents, such as ChatGPT Codex CLI (native support), OpenCode (native support), Aider (configurable via --conventions-file), and Gemini CLI (configurable via settings.json), enabling consistent guidance in multi-tool environments.
• Efficiency and Scalability: Simplifies workflows for teams, minimizes config clutter, and enhances project consistency, especially in large or collaborative setups.

Technical Implementation Details

The change could be implemented with minimal effort (approximately 20-30 lines of code) while maintaining backward compatibility:

• Detection and Loading: During extension activation in src/extension.ts, retrieve the workspace root using vscode.workspace.workspaceFolders. Check for the file with fs.existsSync(root + '/AGENTS.md') and, if present, read its content as UTF-8 text using fs.readFileSync.
• Integration: Append the natural language content to system prompts in src/llm/promptBuilder.ts or inject it as a default Custom Mode in src/modes/modeProvider.ts (e.g., prompt += \n\nProject Guidelines: ${agentsContent}).
• Configuration: Add a toggle setting in package.json, such as "useAgentRules": { "type": "boolean", "default": true, "description": "Enable loading of AGENTS.md from project root for Agent Rules standard." }, to allow users to opt out.
• Testing: Update tests in src/tests/ by mocking fs to verify content inclusion in prompts, ensuring no regressions for existing modes.

This approach ensures AGENTS.md is treated as an additional source of guidance, processed in conjunction with current configs.

[kevinvandijk]

Hi @sgryphon,

AGENTS.md support was added in 4.73.0!