Claude Skills are awesome, maybe a bigger deal than MCP
by Simon Willison
The essay that framed how practitioners think about Skills — and why a folder of Markdown beats a protocol.
Overview
Posted 16 October 2025, the day Anthropic shipped Skills, Simon Willison's essay is the piece that framed how most practitioners now reason about the feature. It runs in six sections: trying out the slack-gif-creator skill, why Skills depend on a coding environment, Claude Code as a general agent, Skills compared to MCP, the wave of Skills that followed, and a closing argument that the simplicity is the point. The technical claim at its centre is architectural: a Skill is just a folder holding a Markdown file with YAML frontmatter metadata, plus optional scripts and resources. Only the name and description are pre-loaded — Willison puts this at a few dozen extra tokens per Skill — and the body is read only once the model decides the Skill is relevant. He contrasts that with MCP, noting that GitHub's official MCP server alone famously consumes tens of thousands of tokens of context before doing any work, and argues Skills need no protocol specification, no server and no baked-in client support to be portable across models. He is equally explicit about the catch: Skills require filesystem access and the ability to execute commands, so they work inside coding agents like Claude Code and not in a plain API call. The worked example is the slack-gif-creator skill, including a validator enforcing Slack's 2MB limit. The post drew 738 points and 370 comments on Hacker News.
At a Glance
- Topic
- Skills
- Level
- Intermediate
- Format
- Guide
- Cost
- Free
- Duration
- ~20 min read
- Provider
- Simon Willison
- Hands-on
- No
- Certificate
- None
What You’ll Learn
- ✓Explain the SKILL.md folder format and the role of its YAML frontmatter metadata
- ✓Describe progressive disclosure and why it keeps per-skill token cost near zero
- ✓Compare the context cost of a Skill against a typical MCP server's tool definitions
- ✓Identify the runtime prerequisite Skills carry: filesystem access plus command execution
- ✓Judge when a capability belongs in a Skill versus behind an MCP server
- ✓Follow a concrete worked example — the slack-gif-creator skill and its size validator
Highlights
- •Published the day Skills launched and still the most-cited framing of the feature
- •738 points and 370 comments on Hacker News — the practitioner counter-arguments are in that thread
- •Names the constraint most launch coverage skipped: Skills need a code execution environment
- •Makes a concrete token-cost comparison rather than an abstract 'MCP is bloated' assertion
- •Written by the co-creator of Django and author of the LLM CLI, who tested the feature hands-on before writing
Who It’s For
Best For
- ✓Engineers deciding whether to build an MCP server or ship a Skill
- ✓Platform teams standardising how internal agent capabilities are packaged and shared
- ✓Claude Code users who want the design rationale behind Skills, not just the syntax
Prerequisites
- •Know what an LLM context window is and why token budget matters
- •Rough familiarity with MCP servers and LLM tool calling
FAQ
What is Claude Skills are awesome, maybe a bigger deal than MCP?
Simon Willison's launch-day analysis of Claude Skills, and still the most-cited framing of them. It explains the SKILL.md format, progressive disclosure and the token-cost argument against MCP, then names the constraint most coverage skipped: Skills only work where the model has a filesystem and can run commands.
Is Claude Skills are awesome, maybe a bigger deal than MCP free?
Claude Skills are awesome, maybe a bigger deal than MCP is free to access.
What level is Claude Skills are awesome, maybe a bigger deal than MCP for?
Claude Skills are awesome, maybe a bigger deal than MCP is aimed at a intermediate audience. Recommended background: Know what an LLM context window is and why token budget matters, Rough familiarity with MCP servers and LLM tool calling.
How long does Claude Skills are awesome, maybe a bigger deal than MCP take?
Expect roughly ~20 min read. Most learners work through it at their own pace.
What will I learn from Claude Skills are awesome, maybe a bigger deal than MCP?
You'll learn: Explain the SKILL.md folder format and the role of its YAML frontmatter metadata; Describe progressive disclosure and why it keeps per-skill token cost near zero; Compare the context cost of a Skill against a typical MCP server's tool definitions; Identify the runtime prerequisite Skills carry: filesystem access plus command execution; Judge when a capability belongs in a Skill versus behind an MCP server; Follow a concrete worked example — the slack-gif-creator skill and its size validator.
Topics
Sources
This page was written from 2 sources, 1 on domains other than simonwillison.net.