Limits and constraints

Request limits

• Maximum Skills per request: 20

• Maximum Skill upload size: 30 MB (all files combined, uncompressed)

• YAML frontmatter requirements:

  • name: Maximum 64 characters, lowercase letters/numbers/hyphens only, no XML tags, no reserved words ("anthropic", "claude")
  • description: Maximum 1024 characters, non-empty, no XML tags

Environment constraints

Skills run in the code execution container with these limitations:

• No network access: Cannot make external API calls
• No runtime package installation: Only pre-installed packages available
• Isolated environment: A fresh container is created unless you specify an existing container ID

See Code execution tool for available packages.

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