18% of exam score
Tool Design & MCP Integration
Overlooked. Tool descriptions matter more than you think.
Designing tool schemas and descriptions, MCP architecture (host/client/server), MCP primitives (tools, resources, prompts), transports, security, and production patterns.
Key insight
Tool descriptions are the primary mechanism Claude uses for tool selection — not an afterthought. Vague or overlapping descriptions cause misrouting, and the correct first fix is ALWAYS better descriptions, not a routing classifier or few-shot examples.
The exam rewards
- A strong tool description specifies: what it does, expected input formats, example queries it handles well, and explicit boundaries versus similar-looking tools
- When misrouting occurs, improve descriptions FIRST — before adding few-shot examples, routing classifiers, or consolidating tools
- Scope each subagent to 4-5 tools relevant to its role; giving one agent 18 tools degrades selection reliability
- Know tool_choice modes: 'auto' (model may return text), 'any' (must call SOME tool), forced name (must call THIS tool)
- Evaluate existing community MCP servers before building custom ones; only build custom for workflows community servers can't handle
Common anti-patterns
- Near-identical tool descriptions causing constant misrouting between similar tools
- Giving all agents access to all available tools
- Building a custom MCP server before checking community servers
- Using Glob to search file contents, or Grep to match file names — pick the right tool for the job