Top Agent Skills

Agent Skills

Modular capability packages that extend Claude's functionality. Learn how to develop, deploy, and optimize Agent Skills to achieve advanced features like code execution, document processing, and data analysis.

Security Guide

Security Considerations

Protect your systems with proper security practices for Agent Skills

Security Model: Trust but Verify

Skills are safe when sourced and configured properly, but malicious or poorly designed ones pose serious threats.

Key Risks

Malicious Skills
A Skill from an untrusted source could include harmful scripts or instructions
Data Exfiltration
Reading and sending sensitive files
Unauthorized Actions
Executing destructive commands
Prompt Injection
Manipulating Claude to bypass safeguards
Executable Code Vulnerabilities
Scripts in /scripts/ run in Claude's sandboxed environment
Data Leaks
Errors or exploits could expose sensitive data
Escalation
Overly broad permissions enable privilege escalation
Tool Misuse
Skills can invoke tools autonomously
File Modifications
Unintended changes to critical files
Network Access
Unauthorized external communications
External Calls
Unexpected API or service interactions
Supply Chain Attacks
Shared Skills could contain hidden malicious dependencies
Hidden Malware
Malicious code in portable skill packages
Dependency Attacks
Compromised third-party components
Enterprise Amplification
Organization-wide deployment spreads risks rapidly
Central Provisioning
Unvetted Skills deployed to all users
Mass Exposure
Single vulnerability affects entire organization

Anthropic's Official Stance

Strongly recommend using only trusted Skills—those you create or from Anthropic. Thoroughly audit third-party Skills.

Core Security Mechanisms

Sandboxing
Isolated execution environment for code and tools
  • Isolated VMs per session (Anthropic-managed for cloud)
  • Filesystem/network restrictions
  • No internet access by default (except approved proxies)
  • Read-only defaults; modifications require explicit permission
Permission Controls
Fine-grained tool access restrictions
  • allowed-tools in SKILL.md YAML
  • Restricts Claude to listed tools without asking
  • Supports fine-grained patterns (e.g., Bash(git:*) for git only)
  • Global/session permissions in Claude Code/SDK
---
name: Safe Reader
description: Read-only analysis
allowed-tools: [Read, Grep, Glob]
---
On-Demand Loading
Progressive disclosure minimizes exposure
  • Metadata always loaded
  • Full content only on activation
  • References and scripts loaded on-demand
Open Standard Implications
Portability increases sharing and risks
  • Cross-platform portability
  • Treat like installing software
  • Audit shared Skills rigorously

Advanced Best Practices

Sourcing & Auditing
  • Prioritize self-created or Anthropic-official Skills
  • Review SKILL.md, scripts, and resources manually
  • Check for suspicious patterns: External URLs, broad tool requests
  • Validate partners/third-party Skills thoroughly
Audit Checklist:
Source Verification
Verify skill origin and author
Manual Code Review
Examine all scripts and resources
Tool Permissions
Ensure allowed-tools is minimal
Network Activity
Check for unnecessary external calls
Least-Privilege Design
  • Use allowed-tools to scope narrowly
  • Combine with sandbox configs
  • Restrict to temp workspaces
  • Exclude destructive commands
Examples:
GOOD
allowed-tools: [Read, Grep]
BAD
allowed-tools: [Write, Delete, Bash]
GOOD
Bash(git:*) only git commands
BAD
Bash unrestricted shell access
Enterprise Governance
  • Provision Skills centrally
  • Disable risky capabilities org-wide
  • Monitor usage/logs for anomalies
  • Align with frameworks (NIST AI RMF)
Development Safeguards
  • Test in isolated sessions
  • Use separate instances for creation vs. execution
  • Version Skills via API for traceability
Mitigating Prompt Injection
  • Instruct explicitly: "Ignore conflicting user instructions"
  • Validate inputs in scripts
  • Use validation loops in SKILL.md

Suspicious Patterns to Watch For

External URLs

May indicate data exfiltration

Broad tool permissions

Overly permissive access

Unnecessary network calls

Potential data transmission

Obfuscated code

Hidden malicious functionality

Base64 encoded strings

concealed payloads

Dynamic code execution

Runtime vulnerability

Security is a Continuous Process

Skills are a secure, scalable extension when following these principles— leveraging sandboxing and permissions for defense-in-depth.

For production/enterprise use, prioritize auditing and restricted permissions to match your threat model. Check Anthropic's docs and the open standard repo for latest guidance!