capabilities

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the full behavioral burden and does so well. It discloses that the tool does not spawn agents, does not probe agents, and provides the exact model resolution order. This gives the agent a strong mental model of the tool's behavior without needing annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is front-loaded with the core purpose and then provides tightly relevant details: roster contents, model resolution, and the doctor alternative. Every sentence earns its place; there is no filler or redundant restatement.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool has no parameters and an output schema exists, the description covers everything an agent needs: what the roster contains, how models are resolved, that it is static/non-probing, and which sibling to use for live model ids. The context is fully sufficient for correct selection and invocation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool has zero parameters, so parameter semantics are largely moot. The description adds value by explaining what each returned agent includes and how model resolution works, which compensates for having no parameters to document.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb ('List') and resource ('ACP agents Rutherford can drive'), and immediately distinguishes this tool from actions by noting it is a 'static roster; no spawn'. This clearly separates it from sibling tools like doctor and delegate.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explicitly tells the agent when NOT to use this tool: 'For live advertised model ids, use doctor(agent=<id>, connect_only=true)'. It also clarifies that capabilities is for static roster information and never probes agents, giving clear routing guidance relative to siblings.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.