Update a phone number

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

The description adds behavioral context beyond the all-false annotations by disclosing the scope requirement (`phone_numbers:write`) and the partial-update semantics ('Only the fields you send are changed'). However, it does not describe side effects, return behavior, or idempotency, and the mutation's other consequences remain undisclosed.

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 compact and front-loaded: the core action and partial-update behavior appear first, folowed by the scope requirement. It contains no fluff, though the use of 'label' and 'trunk' instead of the actual parameter names introduces minor ambiguity. Efficient for an agent to parse.

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?

For a 5-parameter mutation with no output schema and minimal annotations, the description covers purpose, partial update, and auth, but omits usage boundaries, full parameter list in natural language, and return/error behavior. The sibling list offers related phone-number tasks, but no routing guidance is provided. Adequate but not complete.

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?

Schema description coverage is only 40%, and the description compensates for the undocumented `name`, `sip_trunk_id`, and `inbound_agent_id` by referring to them as 'label, trunk or inbound agent'. The `id` and `phone_number` are already described in the schema. The description does not clarify that `phone_number` itself is also updatable, but overall it adds meaningful mapping for the otherwise undocumented fields.

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 uses a specific verb ('Change') and resource ('a phone number') and enumerates the updatable fields ('label, trunk or inbound agent'). This distinguishes it from same-resource siblings like create_phone_number and delete_phone_number, though it doesn't explicitly contrast with other update_* tools. The title already identifies the resource, so the description adds useful field-level clarity.

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?

No when-to-use or when-not-to-use guidance is given, and no alternatives are mentioned. The description notes partial-update behavior and the required scope, but an agent must infer from sibling names when to choose update_phone_number versus create_phone_number or update_sip_trunk. There is no explicit exclusion or alternative routing.

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