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System Prompts & Rules
AGENTS.md, Cursor Rules, Spec Kit, OpenSpec, and the SKILL.md spec: portable instruction and spec formats for AI coding agents.
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Almost nothing on this page is a product. These entries are rules files, repository instruction formats, and spec formats: things you read and copy into your own repo, not things you install and pay for. That is why pricing tiers and benchmark scores do not apply here, and why none of these entries carries a Score.
The core of the shelf is portable conventions. AGENTS.md tells any coding agent how to build, test, and behave in your project. Cursor Rules are project rules stored as .mdc files in .cursor/rules, scoped to your codebase and kept under version control. Spec Kit and OpenSpec add a lightweight spec layer so developers and agents agree on what to build before any code is written. The open Agent Skills specification (SKILL.md) sits alongside them as the packaging format for reusable skill folders; the skill packs and registries that use it are listed on the parent Agent Skills & Prompts page.
When choosing, prefer an open convention (AGENTS.md, SKILL.md, Cursor Rules, Spec Kit, or OpenSpec) over a pack written for a single assistant when the same instructions need to work across several agents, and treat any adoption count as the maintainer's own figure until you verify it.
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Open standard for guiding AI coding agents at the repository level
AGENTS.md is an open standard format adopted by 60,000+ open-source projects for providing AI coding agents with repository-level instructions. With 20,000+ GitHub stars, it has been adopted by GitHub Copilot, OpenAI Codex, Google Gemini CLI, and multiple IDEs as the de facto way to communicate project context and coding conventions to AI agents.
Open standard for portable skills across AI agents
Agent Skills is the open SKILL.md folder specification for packaging reusable instructions, scripts, references, and assets that compatible AI agents load through progressive disclosure. Originally developed by Anthropic and released as an open standard, it defines the portable format itself—not an example library, marketplace, or hosted agent product.
Community cursor rules directory
Community-maintained collection of .cursorrules files that customize Cursor IDE's AI behavior for specific frameworks, languages, and project types. Define coding conventions, preferred libraries, architectural patterns, and style guidelines that the AI follows consistently. Popular rules exist for Next.js, React, Python, TypeScript, Tailwind, and more. Hosted on cursor.directory with 1-click installation. Essential for getting consistent, project-aware AI completions in Cursor.
Spec-driven development for AI coding assistants
OpenSpec is an open-source spec-driven development framework by Fission-AI for AI coding assistants. It adds a lightweight spec layer so developers and AI agents agree on what to build before any code is written. OpenSpec organizes changes in dedicated folders for proposals, specs, design docs, and tasks, and works across 21+ AI coding tools including Claude Code, Cursor, Windsurf, Continue, Gemini CLI, GitHub Copilot, and Amazon Q — bringing structured planning to agentic development.
Toolkit for spec-driven development with AI
GitHub's official toolkit for spec-driven development. Write specifications in natural language and let AI coding agents implement them with structure, consistency, and traceability. Bridges the gap between product requirements and AI-generated code by providing a standardized format that agents can follow reliably across complex projects.
Community tiers
A different perspective: rank the tools you know from S to D.
Sources & verification
- AGENTS.md
- Agent Skills specification
- Cursor docs: Rules
- github/spec-kit (GitHub)
- Fission-AI/OpenSpec (GitHub)
Verification dates are editorial checks. Routine CMS saves and automatic updatedAt timestamps do not advance them.