Register a phone number

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

Annotations only provide false hints, so the description carries the full burden of behavioral disclosure. It clearly states that inbound calls are rejected if inbound_agent_id is not set, that carrier-level configuration is required for inbound to work, that numbers must already be owned (Wixzel does not sell them), and that the phone_numbers:write scope is required. These are concrete, useful behavioral details beyond what the schema or annotations convey.

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 main purpose is in the first sentence, followed by the critical behavioral caveat, the carrier prerequisite, and the required scope. Every sentence adds value with 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?

For a create operation with four parameters and no output schema, the description adequately covers the intended use, prerequisite configuration, optional-agent behavior, and required permission. It references get_sip_trunk for the origination_uri detail, making it complete enough for an agent to select and invoke the tool correctly.

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 100%, so the baseline is 3. The description adds meaningful semantics for inbound_agent_id by explaining that omitting it means inbound calls are rejected, which goes beyond the schema's 'Agent that answers inbound calls to this number.' The other parameters are adequately defined by the schema, so a slight elevation to 4 is justified.

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, 'Register', and clearly identifies the resource: a number you already own, attached to one of your SIP trunks. It also distinguishes the tool from the sibling set by explicitly noting that Wixzel does not sell numbers, while the create/list/update/delete siblings in the phone number group make the intent unambiguous.

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 gives clear context: use this when you own a phone number and want to register it on a SIP trunk. It also provides actionable preconditions for inbound calling—set inbound_agent_id for an agent to answer, and point the carrier at the trunk's origination_uri for inbound to ring at all. However, it does not explicitly mention alternative siblings (e.g., update_phone_number) for subsequent changes, so it stops short of a perfect score.

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