When Claude Code shipped SKILL.md support earlier this year, it felt niche. A convention for describing what an AI agent can do, discoverable at runtime. Interesting, but limited to one tool.
That's changed. SKILL.md is now supported across OpenAI Codex CLI, GitHub Copilot, Cursor, and Vercel — plus at least 7 commercial enterprise partners. What started as an Anthropic-specific convention has become the closest thing the agent ecosystem has to a package standard for capabilities.
This post covers what SKILL.md is, what the multi-ecosystem shift means, and how to write one.
What SKILL.md is
SKILL.md is a markdown file that describes a discrete capability an AI agent can acquire at runtime. The file lives in a skill package, is human-readable, and follows a convention that agent tools know to look for.
When an agent encounters a npx skills install command, or discovers a skill in a marketplace, it reads the SKILL.md to understand:
- What the skill does
- What inputs it expects
- What outputs it produces
- How to invoke it
Think of it like a README, but for agents rather than humans. Structured enough for a tool to parse, readable enough for a developer to review.
The multi-ecosystem jump
Here's the sequence:
- Claude Code started supporting SKILL.md — agents running in Claude Code environments could discover and install skills.
- OpenAI Codex CLI added support. Same file format. Agents in Codex environments could read the same SKILL.md files.
- GitHub Copilot followed. Same pattern.
-
Cursor, Vercel, and a set of enterprise tools adopted it. The install pattern
npx skills install <skill-name>became consistent across all of them.
Seven enterprise partners supporting a common format isn't a trend — it's a standard forming in real time.
Why this matters for developers
Before SKILL.md, if you built a specialized capability — a code review protocol, a financial risk assessment, a DeFi yield scanner — you had roughly two options: build a full API with auth and billing, or give it away for free.
Neither works well for agent-native tools. Agents don't sign up for things. They don't maintain sessions. They just need to call capabilities and pay for them programmatically.
SKILL.md combined with payment protocols like x402 changes this. A skill package with a SKILL.md file can be:
- Discovered by any compatible agent tool
- Installed at runtime with one command
- Paid for per-use in USDC without human sign-up flows
The developer writes the skill once. Any agent tool that supports the standard can consume it.
How to write a SKILL.md
A minimal SKILL.md has five sections:
# Skill Name
## Description
What this skill does in 2-3 sentences.
## Capabilities
- Capability 1
- Capability 2
- Capability 3
## Usage
npx skills install your-skill-name
## Integrates With
Claude Code, Codex CLI, Cursor, GitHub Copilot
Keep it factual. Agents parse this to understand what to do with the skill — not to be sold on it. Shorter is better. Precision matters more than completeness.
A few things that make skills more discoverable:
- Specific capability names (not "analyzes code" but "detects cyclomatic complexity above threshold and flags for refactor")
- Concrete output format (what does the skill return?)
- Integration list (which tools support it?)
Live examples
ClawMerchants has a set of working SKILL.md-based skills available now. Two that are directly useful for agent development:
Agent Financial Planning — budget allocation, ROI modeling, and cost forecasting for agent systems
npx skills install agent-financial-planning-skill
Agent Code Review Protocol — code quality analysis, security-aware review, test coverage gap detection, PR comment generation. Multi-language: TypeScript, Python, Go, Rust.
npx skills install agent-code-review-skill
Both are x402-gated — agents pay per use in USDC. No sign-up, no API keys, no OAuth flows.
The pattern to watch
The npx skills install convention is becoming the npm install moment for agent capabilities. If you're building something agents could use — a data feed, a specialized review tool, a domain-specific analysis — wrapping it as a SKILL.md-compatible package puts it in front of every agent tool that supports the standard.
That's a distribution channel that didn't exist six months ago.
Try it:
npx skills add danielxri/clawmerchants-skills
Or browse: clawmerchants.com
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