What Skills are (and why they change everything)

TL;DR

A Skill is a folder with instructions, scripts, and examples that Claude loads on its own when the request fits. It’s like having specialist virtual employees — finance, legal, sales — all living inside the same AI.

The mechanic in one sentence

Skill = folder with SKILL.md + (optional) scripts and reference files. Claude detects relevance by name and description. Loads only what’s needed, exactly when needed.

How it works under the hood (3 loading levels)

This is the secret. A Skill doesn’t take up conversation context the entire time.

Level 1 — Metadata (always loaded)

Just the skill name and description (~100 tokens). Negligible cost.

---
name: financial-analysis
description: Analyzes P&L, cash flow, runway. Use when the user asks for analysis of a financial spreadsheet, projection, or company health diagnosis.
---

Claude knows this skill exists. It doesn’t know how to use it yet.

Level 2 — Instructions (loads when activated)

When you ask “analyze my P&L,” Claude reads the entire SKILL.md. Under 5K tokens.

# Financial Analysis

## Quick start
1. Identify if it's P&L, cash flow, or balance sheet.
2. For P&L: calculate gross margin, operating margin, EBITDA.
3. For cash flow: calculate runway and burn rate.
4. Compare with sector benchmarks.

## Gotchas
- Watch for outliers in bonus months.
- Deferred revenue is not recognized revenue.

Level 3 — Resources (loads only if needed)

Python scripts, Excel templates, reference spreadsheets. They live in the folder but only enter context if called.

financial-analysis/
├── SKILL.md
├── sector-benchmarks.json
├── scripts/
│   ├── calculate_runway.py
│   └── project_pl.py
└── templates/
    └── executive-report.md

Result: you can have dozens of skills installed without inflating context.

Skills that come ready-made (built-in)

Anthropic packaged 4 critical skills for business work:

• xlsx — creates Excel spreadsheets with working formulas
• docx — creates formatted Word documents
• pptx — generates PowerPoint presentations
• pdf — generates structured PDFs

You don’t have to configure anything. You ask for “create an executive report in Excel with charts” — it uses the xlsx skill automatically.

How to create your first skill (5 minutes)

In Claude.ai

1. Go to Settings → Features → Skills
2. Enable Code execution (required)
3. Click Create Skill or upload a .zip

In Claude Code (terminal)

mkdir -p ~/.claude/skills/sales-analysis
cd ~/.claude/skills/sales-analysis

Create a SKILL.md:

---
name: sales-analysis
description: Analyzes the sales funnel, identifies bottlenecks, and calculates CAC/LTV. Use when the user sends a sales spreadsheet, CRM export, or asks about sales performance.
---

# Sales Analysis

## When to use
- Spreadsheet of leads / opportunities
- CRM export (HubSpot, Pipedrive, RD)
- Question about conversion, CAC, LTV

## How to analyze

1. **Identify the funnel structure**
   - Stages present
   - Volume at each stage
   - Conversion rate between stages

2. **Calculate KPIs**
   - Overall conversion (lead → sale)
   - Average ticket
   - CAC (if cost data exists)
   - LTV (if there's a retention period)
   - Average sales cycle

3. **Find bottlenecks**
   - Where is the drop greater than 60% between stages?
   - Which rep is an outlier?
   - Which lead source converts least?

4. **Report format**
   - Executive summary (3 bullets)
   - KPI table
   - 3 critical patterns
   - 30-day action plan

Done. Next time you toss in a sales spreadsheet, Claude uses this skill automatically.

Where the same skill works

It works on three surfaces (with slight differences):

Surface	Support	How
claude.ai	Custom + built-in	Upload zip via Settings
API	Custom + built-in	Endpoint /v1/skills
Claude Code	Custom (filesystem)	Folder ~/.claude/skills/ or .claude/skills/

Important: skills don’t sync between surfaces. If you create one in claude.ai, you need to upload it separately for the API.

Critical gotchas

• Skill name: lowercase, hyphens, no special characters. Max 64 characters.
• Description is what matters: Claude picks the skill by description, not by name. Put effort here.
• Security: skills run code. Never install a skill from an unknown source without auditing. Malicious skills can leak data.
• Don’t use in the name: “anthropic” or “claude” (reserved words).
• Costs: each activated skill consumes session tokens. Don’t create a skill that loads a giant file unnecessarily.

What this is for in your company

Real use cases:

• Skill “sales-diagnosis” — every manager who drops a CRM export gets analysis in the same format.
• Skill “contract-review” — checks risky clauses in contract PDFs.
• Skill “investor-email” — writes monthly investor updates in the right tone.
• Skill “tax-audit” — analyzes electronic invoices (NF-e, the Brazilian electronic invoice standard) and flags inconsistencies.

Each skill created = hours of repetitive work eliminated, with consistent quality.

Next step

See how to connect Claude to the systems your company already uses — Drive, Gmail, HubSpot, Notion.