Anthropic Skills (anthropics/skills)

Anthropic Skills

https://github.com/anthropics/skills
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Anthropic Skills are folders of instructions, scripts, and resources that Claude loads dynamically...

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# Anthropic Agent Skills

Anthropic Agent Skills is a comprehensive collection of skills that teach Claude how to complete specialized tasks in a repeatable way. Skills are folders containing instructions, scripts, and resources that Claude loads dynamically to improve performance on specific tasks—from creating documents with brand guidelines to analyzing data with organizational workflows, building MCP servers, or creating visual art. Each skill is self-contained in its own folder with a `SKILL.md` file containing YAML frontmatter (name, description) and markdown instructions that Claude follows when the skill is active.

This repository demonstrates what's possible with Claude's skills system, ranging from creative applications (algorithmic art, canvas design, theme styling) to technical tasks (webapp testing, MCP server generation) to enterprise workflows (document creation, internal communications). The repository is organized into three main sections: `/skills` containing all skill implementations, `/spec` linking to the Agent Skills specification, and `/template` providing a starter template for creating new skills. Skills can be used via Claude Code (as plugins), Claude.ai (native support for paid plans), or the Claude API.

---

## Creating a Basic Skill

A skill requires only a `SKILL.md` file with YAML frontmatter containing `name` and `description` fields, followed by markdown instructions.

```markdown
---
name: my-skill-name
description: A clear description of what this skill does and when to use it
---

# My Skill Name

[Add your instructions here that Claude will follow when this skill is active]

## Examples
- Example usage 1
- Example usage 2

## Guidelines
- Guideline 1
- Guideline 2
```

---

## Installing Skills in Claude Code

Skills can be installed as plugins from the Anthropic marketplace using Claude Code CLI commands.

```bash
# Add the Anthropic skills marketplace
/plugin marketplace add anthropics/skills

# Install document processing skills (PDF, DOCX, XLSX, PPTX)
/plugin install document-skills@anthropic-agent-skills

# Install example skills (algorithmic art, MCP builder, webapp testing, etc.)
/plugin install example-skills@anthropic-agent-skills

# Install Claude API skill
/plugin install claude-api@anthropic-agent-skills
```

---

## PDF Processing

The PDF skill enables reading, extracting, merging, splitting, rotating, watermarking, encrypting, and creating PDF files using Python libraries and command-line tools.

```python
from pypdf import PdfReader, PdfWriter
import pdfplumber

# Read and extract text from PDF
reader = PdfReader("document.pdf")
print(f"Pages: {len(reader.pages)}")

text = ""
for page in reader.pages:
    text += page.extract_text()

# Extract tables using pdfplumber
with pdfplumber.open("document.pdf") as pdf:
    for page in pdf.pages:
        tables = page.extract_tables()
        for table in tables:
            print(table)

# Merge multiple PDFs
writer = PdfWriter()
for pdf_file in ["doc1.pdf", "doc2.pdf", "doc3.pdf"]:
    reader = PdfReader(pdf_file)
    for page in reader.pages:
        writer.add_page(page)

with open("merged.pdf", "wb") as output:
    writer.write(output)

# Create new PDF with reportlab
from reportlab.lib.pagesizes import letter
from reportlab.pdfgen import canvas

c = canvas.Canvas("hello.pdf", pagesize=letter)
width, height = letter
c.drawString(100, height - 100, "Hello World!")
c.save()

# Add password protection
reader = PdfReader("input.pdf")
writer = PdfWriter()
for page in reader.pages:
    writer.add_page(page)
writer.encrypt("userpassword", "ownerpassword")
with open("encrypted.pdf", "wb") as output:
    writer.write(output)
```

---

## Word Document (DOCX) Creation

The DOCX skill creates and edits Word documents using the docx-js library with support for styles, tables, images, headers/footers, and table of contents.

```javascript
const { Document, Packer, Paragraph, TextRun, Table, TableRow, TableCell,
        Header, Footer, HeadingLevel, PageNumber, PageBreak,
        BorderStyle, WidthType, ShadingType, AlignmentType } = require('docx');
const fs = require('fs');

const doc = new Document({
  styles: {
    default: { document: { run: { font: "Arial", size: 24 } } }, // 12pt default
    paragraphStyles: [
      { id: "Heading1", name: "Heading 1", basedOn: "Normal", next: "Normal",
        run: { size: 32, bold: true, font: "Arial" },
        paragraph: { spacing: { before: 240, after: 240 }, outlineLevel: 0 } },
    ]
  },
  sections: [{
    properties: {
      page: {
        size: { width: 12240, height: 15840 }, // US Letter in DXA
        margin: { top: 1440, right: 1440, bottom: 1440, left: 1440 } // 1 inch
      }
    },
    headers: {
      default: new Header({ children: [new Paragraph({ children: [new TextRun("Company Report")] })] })
    },
    footers: {
      default: new Footer({ children: [new Paragraph({
        children: [new TextRun("Page "), new TextRun({ children: [PageNumber.CURRENT] })]
      })] })
    },
    children: [
      new Paragraph({ heading: HeadingLevel.HEADING_1, children: [new TextRun("Annual Report 2024")] }),
      new Paragraph({ children: [new TextRun("This report summarizes our key achievements.")] }),
      new Table({
        width: { size: 9360, type: WidthType.DXA },
        columnWidths: [4680, 4680],
        rows: [
          new TableRow({
            children: [
              new TableCell({
                borders: { top: { style: BorderStyle.SINGLE, size: 1, color: "CCCCCC" } },
                width: { size: 4680, type: WidthType.DXA },
                shading: { fill: "D5E8F0", type: ShadingType.CLEAR },
                children: [new Paragraph({ children: [new TextRun("Metric")] })]
              }),
              new TableCell({
                width: { size: 4680, type: WidthType.DXA },
                children: [new Paragraph({ children: [new TextRun("Value")] })]
              })
            ]
          })
        ]
      }),
      new Paragraph({ children: [new PageBreak()] }),
      new Paragraph({ children: [new TextRun("Page 2 content")] })
    ]
  }]
});

Packer.toBuffer(doc).then(buffer => fs.writeFileSync("report.docx", buffer));
```

---

## Excel Spreadsheet (XLSX) Operations

The XLSX skill creates, edits, and analyzes Excel files using openpyxl with support for formulas, formatting, and LibreOffice-based recalculation.

```python
import pandas as pd
from openpyxl import Workbook, load_workbook
from openpyxl.styles import Font, PatternFill, Alignment

# Read and analyze with pandas
df = pd.read_excel('data.xlsx', sheet_name=None)  # All sheets
print(df['Sheet1'].describe())

# Create new workbook with openpyxl
wb = Workbook()
sheet = wb.active
sheet.title = "Financial Model"

# Add headers with formatting
headers = ['Year', 'Revenue', 'Expenses', 'Profit']
for col, header in enumerate(headers, 1):
    cell = sheet.cell(row=1, column=col, value=header)
    cell.font = Font(bold=True)
    cell.fill = PatternFill('solid', fgColor='D5E8F0')

# Add data with formulas (ALWAYS use formulas, never hardcode calculations)
data = [
    ['2024', 1000000, 750000],
    ['2025', 1200000, 850000],
]
for row_idx, row_data in enumerate(data, 2):
    sheet.cell(row=row_idx, column=1, value=row_data[0])
    sheet.cell(row=row_idx, column=2, value=row_data[1])
    sheet.cell(row=row_idx, column=3, value=row_data[2])
    # Use Excel formula for Profit = Revenue - Expenses
    sheet.cell(row=row_idx, column=4, value=f'=B{row_idx}-C{row_idx}')

# Add summary formulas
sheet['B5'] = '=SUM(B2:B4)'
sheet['C5'] = '=SUM(C2:C4)'
sheet['D5'] = '=B5-C5'

# Format as currency
for row in range(2, 6):
    for col in range(2, 5):
        sheet.cell(row=row, column=col).number_format = '$#,##0'

wb.save('financial_model.xlsx')

# Recalculate formulas with LibreOffice (MANDATORY after adding formulas)
# python scripts/recalc.py financial_model.xlsx
```

---

## PowerPoint Presentation (PPTX) Creation

The PPTX skill creates and edits presentations using pptxgenjs with design guidelines for professional, non-generic slides.

```bash
# Read presentation content
python -m markitdown presentation.pptx

# Generate slide thumbnails for inspection
python scripts/thumbnail.py presentation.pptx

# Convert to PDF then images
python scripts/office/soffice.py --headless --convert-to pdf output.pptx
pdftoppm -jpeg -r 150 output.pdf slide
```

```javascript
const pptxgen = require('pptxgenjs');

let pres = new pptxgen();
pres.layout = 'LAYOUT_16x9';

// Title slide with bold color palette (not generic blue!)
let slide1 = pres.addSlide();
slide1.background = { color: '1E2761' }; // Midnight navy
slide1.addText('Q4 2024 Results', {
  x: 0.5, y: 2.5, w: '90%',
  fontSize: 44, bold: true, color: 'FFFFFF',
  fontFace: 'Georgia'
});
slide1.addText('Annual Performance Review', {
  x: 0.5, y: 3.5, w: '90%',
  fontSize: 24, color: 'CADCFC',
  fontFace: 'Calibri'
});

// Content slide with data callouts
let slide2 = pres.addSlide();
slide2.background = { color: 'FFFFFF' };
slide2.addText('Key Metrics', {
  x: 0.5, y: 0.5, fontSize: 36, bold: true,
  color: '1E2761', fontFace: 'Georgia'
});

// Large stat callouts (not bullet points!)
slide2.addText('$2.4M', {
  x: 1, y: 1.5, fontSize: 60, bold: true,
  color: '1E2761', fontFace: 'Georgia'
});
slide2.addText('Revenue Growth', {
  x: 1, y: 2.5, fontSize: 18, color: '666666'
});

slide2.addText('+34%', {
  x: 5, y: 1.5, fontSize: 60, bold: true,
  color: '2C5F2D', fontFace: 'Georgia'
});
slide2.addText('Year over Year', {
  x: 5, y: 2.5, fontSize: 18, color: '666666'
});

pres.writeFile({ fileName: 'quarterly_results.pptx' });
```

---

## MCP Server Development

The MCP builder skill creates high-quality Model Context Protocol servers that enable LLMs to interact with external services through well-designed tools.

```typescript
// TypeScript MCP Server with Zod schema validation
import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import { z } from "zod";

const server = new McpServer({
  name: "github-mcp",
  version: "1.0.0"
});

// Define tool with Zod schema
const CreateIssueSchema = z.object({
  repo: z.string().describe("Repository in format 'owner/repo'"),
  title: z.string().describe("Issue title"),
  body: z.string().optional().describe("Issue body in markdown"),
  labels: z.array(z.string()).optional().describe("Labels to apply")
});

server.tool(
  "github_create_issue",
  "Create a new issue in a GitHub repository",
  CreateIssueSchema.shape,
  async (params) => {
    const { repo, title, body, labels } = CreateIssueSchema.parse(params);

    const response = await fetch(`https://api.github.com/repos/${repo}/issues`, {
      method: 'POST',
      headers: {
        'Authorization': `token ${process.env.GITHUB_TOKEN}`,
        'Content-Type': 'application/json'
      },
      body: JSON.stringify({ title, body, labels })
    });

    if (!response.ok) {
      throw new Error(`GitHub API error: ${response.status}`);
    }

    const issue = await response.json();
    return {
      content: [{ type: "text", text: `Created issue #${issue.number}: ${issue.html_url}` }]
    };
  },
  {
    annotations: {
      readOnlyHint: false,
      destructiveHint: false,
      idempotentHint: false
    }
  }
);

// Start server with stdio transport
const transport = new StdioServerTransport();
await server.connect(transport);
```

---

## Web Application Testing with Playwright

The webapp-testing skill provides tools for testing local web applications using Playwright with server lifecycle management.

```python
# Start server and run automation
# bash: python scripts/with_server.py --server "npm run dev" --port 5173 -- python test.py

from playwright.sync_api import sync_playwright

with sync_playwright() as p:
    browser = p.chromium.launch(headless=True)
    page = browser.new_page()

    # Navigate and wait for JavaScript to execute
    page.goto('http://localhost:5173')
    page.wait_for_load_state('networkidle')  # CRITICAL: Wait for JS

    # Reconnaissance: discover elements
    page.screenshot(path='/tmp/initial.png', full_page=True)
    buttons = page.locator('button').all()
    print(f"Found {len(buttons)} buttons")

    # Execute actions with discovered selectors
    page.locator('text=Submit').click()
    page.wait_for_selector('.success-message')

    # Capture console logs
    page.on('console', lambda msg: print(f"Console: {msg.text}"))

    # Final screenshot
    page.screenshot(path='/tmp/result.png')
    browser.close()
```

---

## Claude API Integration

The claude-api skill provides documentation and patterns for building LLM-powered applications with Claude using the official SDKs.

```python
# Python SDK with Claude Opus 4.6 and adaptive thinking
import anthropic

client = anthropic.Anthropic()

# Basic completion with adaptive thinking (recommended for Opus 4.6)
response = client.messages.create(
    model="claude-opus-4-6",
    max_tokens=4096,
    thinking={"type": "adaptive"},  # Let Claude decide when/how much to think
    messages=[
        {"role": "user", "content": "Analyze this code for security vulnerabilities..."}
    ]
)
print(response.content[0].text)

# Streaming for long responses (prevents timeouts)
with client.messages.stream(
    model="claude-opus-4-6",
    max_tokens=16384,
    thinking={"type": "adaptive"},
    messages=[{"role": "user", "content": "Write a comprehensive analysis..."}]
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)

# Get final message after streaming
final_message = stream.get_final_message()

# Tool use with automatic loop handling
from anthropic.beta import beta_tool

@beta_tool
def get_weather(location: str) -> str:
    """Get current weather for a location."""
    return f"Weather in {location}: 72°F, sunny"

response = client.beta.messages.create(
    model="claude-opus-4-6",
    max_tokens=1024,
    tools=[get_weather],
    messages=[{"role": "user", "content": "What's the weather in San Francisco?"}]
)
```

```typescript
// TypeScript SDK
import Anthropic from '@anthropic-ai/sdk';

const client = new Anthropic();

// With effort parameter for controlling thinking depth
const response = await client.messages.create({
  model: "claude-opus-4-6",
  max_tokens: 4096,
  thinking: { type: "adaptive" },
  output_config: { effort: "high" }, // low, medium, high, or max (Opus only)
  messages: [
    { role: "user", content: "Explain quantum computing..." }
  ]
});

// Structured output with Zod validation
import { z } from 'zod';

const AnalysisSchema = z.object({
  summary: z.string(),
  sentiment: z.enum(["positive", "negative", "neutral"]),
  confidence: z.number()
});

const parsed = await client.messages.parse({
  model: "claude-opus-4-6",
  max_tokens: 1024,
  output_config: {
    format: {
      type: "json_schema",
      json_schema: { schema: AnalysisSchema }
    }
  },
  messages: [{ role: "user", content: "Analyze this customer review..." }]
});
```

---

## Algorithmic Art Generation

The algorithmic-art skill creates generative art using p5.js with seeded randomness and interactive parameter exploration.

```javascript
// Self-contained HTML artifact with p5.js generative art
// Seed-based randomness ensures reproducibility
let params = {
  seed: 12345,
  particleCount: 1000,
  noiseScale: 0.003,
  flowStrength: 2.0,
  fadeRate: 10
};

let particles = [];

function setup() {
  createCanvas(1200, 1200);
  randomSeed(params.seed);
  noiseSeed(params.seed);
  background(20);

  // Initialize particles
  for (let i = 0; i < params.particleCount; i++) {
    particles.push({
      x: random(width),
      y: random(height),
      prevX: 0,
      prevY: 0
    });
  }
}

function draw() {
  // Subtle fade for trail effect
  fill(20, params.fadeRate);
  noStroke();
  rect(0, 0, width, height);

  // Update and draw particles following flow field
  stroke(255, 50);
  strokeWeight(1);

  for (let p of particles) {
    p.prevX = p.x;
    p.prevY = p.y;

    // Flow field from Perlin noise
    let angle = noise(p.x * params.noiseScale, p.y * params.noiseScale) * TWO_PI * 2;
    p.x += cos(angle) * params.flowStrength;
    p.y += sin(angle) * params.flowStrength;

    // Wrap around edges
    if (p.x < 0) p.x = width;
    if (p.x > width) p.x = 0;
    if (p.y < 0) p.y = height;
    if (p.y > height) p.y = 0;

    line(p.prevX, p.prevY, p.x, p.y);
  }
}

// Regenerate with new seed
function regenerate(newSeed) {
  params.seed = newSeed;
  randomSeed(params.seed);
  noiseSeed(params.seed);
  particles = [];
  for (let i = 0; i < params.particleCount; i++) {
    particles.push({ x: random(width), y: random(height), prevX: 0, prevY: 0 });
  }
  background(20);
}
```

---

## Web Artifacts Builder

The web-artifacts-builder skill creates complex, multi-component claude.ai HTML artifacts using React, Tailwind CSS, and shadcn/ui.

```bash
# Initialize new React project with all dependencies
bash scripts/init-artifact.sh my-dashboard
cd my-dashboard

# Project includes:
# - React 18 + TypeScript + Vite
# - Tailwind CSS 3.4.1 with shadcn/ui theming
# - 40+ shadcn/ui components pre-installed
# - Path aliases (@/) configured

# Edit src/App.tsx to build your artifact

# Bundle to single HTML file for claude.ai
bash scripts/bundle-artifact.sh
# Creates bundle.html - self-contained artifact with all JS/CSS inlined
```

```tsx
// Example React component using shadcn/ui
import { Card, CardHeader, CardTitle, CardContent } from "@/components/ui/card";
import { Button } from "@/components/ui/button";
import { useState } from "react";

export default function Dashboard() {
  const [count, setCount] = useState(0);

  return (
    <div className="p-6 space-y-4">
      <Card>
        <CardHeader>
          <CardTitle>Interactive Dashboard</CardTitle>
        </CardHeader>
        <CardContent className="space-y-4">
          <p className="text-lg">Count: {count}</p>
          <Button onClick={() => setCount(c => c + 1)}>
            Increment
          </Button>
        </CardContent>
      </Card>
    </div>
  );
}
```

---

## Skill Creator Workflow

The skill-creator skill helps create new skills and iteratively improve them through evaluation and refinement.

```json
// evals/evals.json - Test case structure
{
  "skill_name": "document-generator",
  "evals": [
    {
      "id": 1,
      "prompt": "Create a quarterly report for Q4 2024 with revenue of $2.4M and 34% growth",
      "expected_output": "Professional DOCX with formatted tables, charts, executive summary",
      "files": [],
      "assertions": [
        {"name": "has_executive_summary", "type": "contains", "value": "Executive Summary"},
        {"name": "has_revenue_table", "type": "regex", "value": "\\$2\\.4M|\\$2,400,000"},
        {"name": "file_created", "type": "file_exists", "value": "quarterly_report.docx"}
      ]
    }
  ]
}
```

```bash
# Run skill evaluation
python -m scripts.run_eval \
  --eval-set evals/evals.json \
  --skill-path ./my-skill \
  --model claude-opus-4-6

# Aggregate benchmark results
python -m scripts.aggregate_benchmark workspace/iteration-1 --skill-name my-skill

# Launch interactive reviewer
python eval-viewer/generate_review.py workspace/iteration-1 \
  --skill-name "my-skill" \
  --benchmark workspace/iteration-1/benchmark.json

# Optimize skill description for better triggering
python -m scripts.run_loop \
  --eval-set trigger-eval.json \
  --skill-path ./my-skill \
  --model claude-opus-4-6 \
  --max-iterations 5
```

---

## Summary

Anthropic Agent Skills provides a powerful framework for extending Claude's capabilities through modular, reusable skill definitions. The document skills (PDF, DOCX, XLSX, PPTX) enable professional document creation and manipulation with full formatting control. The technical skills (MCP builder, webapp testing, Claude API) support developers building integrations and automated testing workflows. The creative skills (algorithmic art, canvas design, web artifacts) enable sophisticated visual content generation.

The skill system follows a consistent pattern: each skill contains a `SKILL.md` file with metadata and instructions, optional scripts for deterministic operations, and reference documentation for complex tasks. Skills can be combined—for example, using the webapp-testing skill to verify output from the web-artifacts-builder, or using the skill-creator to iteratively improve any skill through evaluation. The system is designed for both consumption (using existing skills) and creation (building custom skills for specific organizational needs), making it adaptable to a wide range of automation and content generation use cases.