Skills (Anthropic)

Skills are "expertise on demand". Instead of loading the entire Excel manual into context, the model loads it ONLY when the user asks something Excel-related. That makes it faster, cheaper, and more precise.

Skill ≠ Tool

• Tool = a function the model calls (read_file, send_email).
• Skill = a bundle with instructions + scripts + examples, loaded into context on demand.
• A Skill MAY contain tools, but it's more: it's the know-how about WHEN and HOW to use them.

Anatomy of a Skill

A Skill, in Anthropic's format, is a folder with a SKILL.md file (instructions + description) and optionally other resources (scripts, templates, examples).

---
name: xlsx
description: Use this skill any time a spreadsheet file is the
  primary input or output. Trigger when the user mentions a
  .xlsx/.csv file by name and wants something done to it.
---

# Spreadsheet manipulation

## When to use
- User uploads a .xlsx file and asks for analysis
- User wants to build a sheet from raw data
- User wants charts, formulas, formatting

## How to operate
1. Use the openpyxl library...
2. Validate column types before...
3. Always preserve formatting unless...

## Pitfalls
- Don't overwrite the original file
- ...

How the model decides

In short, the flow is: the model sees a list of available Skills (just name + description — not full content). When the user writes something, the model "searches" descriptions and — if it finds a match — loads the full Skill.

Real Skill examples

• xlsx — spreadsheet manipulation (analysis, formatting, charts).
• pdf — read, merge, extract text/tables from PDFs.
• ba-po-toolkit — write user stories, gap analysis, BPMN.
• security-review — audit for code vulnerabilities.