Claude Skills are awesome, maybe a bigger deal than MCP

TL;DR Highlight

Anthropic's Claude Skills bundles markdown files and scripts to give LLMs new capabilities.

Who Should Read

Developers who use Claude via API or Claude.ai and want a structured way to add reusable capabilities to their LLM workflows.

Core Mechanics

A Skill is a directory containing a SKILL.md instruction file and optional supporting scripts/resources
Skills are loaded at conversation start and persist for the session
Multiple skills can be combined in a single session for composable functionality
Reduces repetitive prompt engineering by packaging common workflows as reusable units
Anthropic provides a skill registry and tooling for creating/sharing skills

Evidence

Official Anthropic announcement and documentation
Community demonstrations showing skills enabling consistent multi-step workflows
Comparison with raw system prompts shows reduced token usage and higher reliability

How to Apply

Start by converting your most frequently repeated system prompts into skill packages.
Include example inputs and outputs in SKILL.md to guide the LLM's behavior more precisely.
Version control your skills folder alongside your code for reproducibility.

Code Example

snippet

# Example skill directory structure
# my-skill/
#   SKILL.md          <- Description and trigger conditions in frontmatter
#   core/
#     helper.py       <- Utilities the model can call
#   templates/
#     boilerplate.py  <- Template files

# SKILL.md frontmatter example:
# ---
# description: "Toolkit for creating animated GIFs optimized for Slack"
# trigger: "users request animated GIFs or emoji animations for Slack"
# ---

# Pattern used in Python within a skill:
import sys
sys.path.insert(0, '/mnt/skills/examples/slack-gif-creator')
from core.gif_builder import GIFBuilder

# Validate Slack size limit after GIF creation
passes, info = check_slack_size('output.gif', is_emoji=False)
if not passes:
    print(f"⚠ {info['size_kb']:.1f}KB > {info['limit_kb']}KB limit")

Terminology

Skill PackageA folder containing a markdown instruction file and optional scripts/resources that defines a reusable LLM capability.

SKILL.mdThe primary instruction file in a Claude Skill, written in markdown, describing what the skill does and how to use it.

Session ContextThe accumulated conversation history and loaded resources available to the LLM within a single conversation.