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

Annotations already establish this is a safe, non-destructive, closed-world read. The description adds domain context beyond them: 'voiceRuntime=livekit' identifies Dedicated caller numbers that support inboundAssistantId, which is genuine value about what the returned data means.

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?

Two tight sentences, purpose front-loaded before the cross-tool usage note and the field-semantics note. No filler or redundancy.

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?

With an output schema present and no input params, the description covers the remaining gaps well: what the list contains, how to consume it, and what a key returned field signals. It stops just short of describing filtering or ordering behavior.

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?

Zero parameters means there is no input contract to explain, so the baseline is 4. The description instead annotates response fields (number, voiceRuntime) that the schema and output schema leave unexplained at the semantic level.

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?

States a specific verb and resource ('List connected caller phone numbers'), which is clear and distinct from the many other list_* siblings. It doesn't explicitly contrast itself with alternatives like list_calls, but the narrow resource keeps ambiguity low.

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?

Offers a useful downstream hint ('Use number as create_call.from') that tells the agent what to do with the result, but gives no explicit when-to-use/when-not guidance or alternative comparison. Usage is implied rather than spelled out.

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