Overview
For a detailed look at the architecture and real-world applications of Agent Skills, read the engineering blog post: Equipping agents for the real world with Agent Skills.
Skills integrate with the Messages API through the code execution tool. Whether using pre-built Skills managed by Anthropic or custom Skills you've uploaded, the integration shape is identical: both require code execution and use the same container structure.
Using Skills
Skills integrate identically in the Messages API regardless of source. You specify Skills in the container parameter with a skill_id, type, and optional version, and they run in the code execution environment.
You can use Skills from two sources:
| Aspect | Anthropic Skills | Custom Skills |
|---|---|---|
| Type value | anthropic | custom |
| Skill IDs | Short names: pptx, xlsx, docx, pdf | Generated: skill_01AbCdEfGhIjKlMnOpQrStUv |
| Version format | Date-based: 20251013 or latest | Version ID: skver_01AbCdEfGhIjKlMnOpQrStUv or latest |
| Management | Pre-built and maintained by Anthropic | Upload and manage through the Skills API |
| Availability | Available to all users | Private to your workspace |
Both skill sources are returned by the List Skills endpoint (use the source parameter to filter). The integration shape and execution environment are identical. The only difference is where the Skills come from and how they're managed.
Prerequisites
To use Skills, you need:
- Claude API key from the Claude Console
- Code execution tool enabled in your requests
Skills require the code execution tool, so use a model from its model compatibility list.