Tool distribution and tool_choice

• Giving an agent many tools (18 rather than 4 or 5) degrades selection reliability.
• Agents with tools outside their specialisation tend to misuse them (a synthesis agent running searches).
• Scoped access: only the tools needed for the role, plus limited cross-role tools for high-frequency needs.
• tool_choice options: auto (text or tool), any (must call some tool), forced selection of a named tool.
• Generic tools can be replaced with constrained ones, such as load_document that validates URLs instead of fetch_url.

• Restrict each subagent's tool set to its role.
• Replace generic tools with constrained alternatives.
• Provide a scoped cross-role tool (verify_fact) for frequent simple needs while routing complex cases through the coordinator.
• Force a specific tool first with tool_choice, then continue in follow-up turns; use any to guarantee a tool call rather than text.

• "More tools make an agent more capable." Past a handful, they make it less reliable.
• "any forces a particular tool." It only forces some tool call.
• "A prompt rule stops an agent misusing an available tool." Removing the tool is what guarantees it.

Agents handed every tool "just in case", and mandatory first steps left to the prompt instead of forced selection.

• 2.1Tool interfaces and descriptions
• 4.3Structured output with tool use
• 1.3Subagent invocation and context passing