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

Annotations already declare non-read-only, idempotent, open-world and non-destructive, so the safety profile is covered. The description adds value with per-number cost ($1.50/mo vs $59/mo legacy bundles) and the shape of returned capabilities, though it says nothing about what happens when a requested number is unavailable or whether provisioning can be undone.

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?

Three sentences, front-loaded with the operations and then the use case, with no filler. The parenthetical price comparison is slightly promotional but does carry decision-relevant cost information.

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 four-action, seven-parameter tool with no output schema, the description covers what each action does, the geographic scope, the cost, and the returned record fields. Gaps remain around failure modes (number already taken, unsupported country) and the fact that SIP configuration requires an existing numberId.

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 coverage is 100%, and the enum's own description already explains each action and the country/phone-number formats. The description only echoes the same action list and country set, adding no format or constraint detail beyond the schema, so the baseline 3 applies.

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 first sentence names four concrete operations (search E.164 numbers, provision, list, bind to SIP/WebRTC trunk) on a clearly identified resource, so an agent can see the scope immediately. It does not mention the sibling tool telecom_messaging, so the boundary between 'numbers' and 'messaging' is left implicit.

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 second sentence gives an explicit triggering condition: use it when an agent needs a dedicated SMS, WhatsApp Business Cloud, or voice number in the listed countries. It supplies no exclusion or alternative-tool guidance, and never says when to prefer the telecom_messaging sibling instead.

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