The Skills System

What You Need to Know

Before you install a single marketplace plugin, you need to understand what Claude can already do. Cowork ships with a set of built-in Agent Skills — native capabilities for processing Excel spreadsheets, Word documents, PowerPoint presentations, and PDFs — that require no installation, no configuration, and no external dependencies. These skills run locally within Claude's sandboxed environment on your device. The file never leaves your machine.

This matters more than it sounds. A surprising number of Cowork users waste time searching for plugins to handle tasks that Claude can do natively. The exam tests this aggressively: if a question asks about the most efficient way to process a local file, and one of the options is a built-in Agent Skill, that's almost always the correct answer.

Built-in Agent Skills: what Claude can do out of the box

Claude's built-in capabilities cover the file types that dominate professional workflows:

• Excel and CSV — read multi-tab workbooks, perform calculations, create pivot tables, generate charts, clean and transform data, write new spreadsheets
• Word documents — read, edit, create, format with headings and tables, apply consistent styling
• PowerPoint — create slide decks from scratch, modify existing presentations, maintain template formatting
• PDF — extract text and structured data, summarise, cross-reference multiple documents

These aren't bolted-on extras. They're core capabilities that run in the sandboxed VM on your device. When Claude processes a 50 MB Excel file with 12 worksheet tabs, that processing happens locally — the file is never uploaded to Anthropic's servers. This is critical for organisations handling sensitive financial data, client records, or anything subject to compliance requirements.

The FindSkill directory and community marketplace

When Claude's built-in capabilities aren't enough — when you need domain-specific expertise like legal contract review, financial modelling templates, or marketing analytics frameworks — you turn to the marketplace. The Browse Plugins menu inside Cowork is the authoritative source for discovering, reviewing, and installing community-built skills and plugin bundles.

The marketplace is organised by category (productivity, analytics, development, legal, marketing) and each listing shows:

• A description of what the plugin does
• The author or publisher
• Required permissions
• Install count and ratings
• The components included (Skills, Connectors, and/or commands)

Before installing anything from the marketplace, always check: does Claude already handle this natively? Installing a third-party "PDF reader" plugin when Claude has a built-in Document Analysis Skill creates redundancy, potential conflicts, and unnecessary permission grants.

Departmental bundles: pre-configured for roles

Departmental bundles are curated collections of plugins tailored to a specific role or team function. A "Sales Analytics" bundle might include the Apollo Connector for lead data, a lead-scoring Skill, a pipeline reporting template, and slash commands for common CRM actions. Instead of assembling components one by one and configuring each separately, a team installs a single bundle and starts working.

This is particularly valuable for team rollouts (covered in Domain 6). Rather than asking every team member to research, install, and configure their own plugins, an administrator selects the appropriate bundle for each role and provisions it centrally.

Local sandboxed execution: the security guarantee

Every skill — built-in or marketplace-installed — runs locally within Claude's sandboxed environment on your device. This is the same security model you learned about in Domain 1: the sandbox isolates Claude's operations from the rest of your system, and file processing happens without data leaving your machine.

The distinction between local skill execution and Connector-based external access is critical:

• Skills process data locally inside the sandbox — no network calls, no data uploaded
• Connectors reach outside the sandbox to query external services via MCP — this is the only way to access data beyond your local machine

If a Skill could make network calls, the entire security model would collapse. Skills are deliberately constrained to local processing precisely because that constraint is what makes them safe to run on sensitive data.

Trust and verification: not all marketplace skills are equal

This is a significant security consideration that the exam tests. Built-in Agent Skills carry Anthropic's implicit quality guarantee. Community skills carry the author's reputation — nothing more. Treat marketplace skills like you would treat a Chrome extension from an unknown developer: useful, potentially excellent, but warranting due diligence before you let it near your data.

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Common Mistakes

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Hands-On Activity

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Practice Question

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Sources

• Use plugins in Cowork — Anthropic
• Cowork: Claude Code power for knowledge work — Anthropic
• Get started with Cowork — Anthropic
• Claude Cowork Guide 2026: Skills, Plugins, Connectors — FindSkill.ai