2.4Phase 4: Invocation

When Claude decides to use a skill, it calls the Skill tool:

{
  "tool": "Skill",
  "input": {
    "skill": "playwright-cli"
  }
}

The system then performs several operations:

4a. Visibility Message (Shown to User)

<command-message>The "playwright-cli" skill is loading</command-message>
<command-name>playwright-cli</command-name>

This appears in the user's chat interface, providing transparency about what's happening.

4b. Context Injection (Hidden from User, Sent to API)

The full content of SKILL.md is injected as a user message with isMeta: true:

• Visible to Claude — it receives the full instructions
• Hidden from UI — the user doesn't see the raw markdown
• Added to conversation history — persists for the remainder of the skill's execution

4c. Permission Elevation

If the SKILL.md frontmatter specifies allowed-tools: Bash, the Bash tool is temporarily pre-approved. This means:

• The agent can run playwright-cli open <url> without asking permission for each command
• The user isn't bombarded with "Allow Bash?" prompts during browser automation
• Permissions revert after the skill completes

4d. Model Override (Optional)

If the SKILL.md specifies a model: field, the system switches to that model for the skill's execution. This enables cost optimization — a simple skill can use Haiku while the main conversation uses Opus.