2.3Phase 3: Selection

When a user message arrives, Claude's language model processes:

• The user's message
• Conversation history
• All available tools (including the Skill tool with its embedded skill list)

There is no algorithmic routing. The selection happens inside Claude's forward pass through the transformer. Claude reads the skill descriptions and decides — through language understanding — whether any skill matches the user's intent.

This means:

• Skill descriptions are the selection mechanism — poorly written descriptions = skills that never get invoked
• Claude may choose not to use a skill even when one is available (if direct tool use seems better)
• Claude may invoke multiple skills sequentially in complex workflows

Selection Signals

Claude considers:

1. Description match — Does the skill description match the user's intent?
2. Conversation context — Has the user been working on browser testing? Then the browser skill is more likely
3. Explicit invocation — User says /playwright-cli or "use the browser skill"
4. Task context — If the agent is writing tests that need browser verification