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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds domain context by clarifying that these are numbers the business 'proved it controls' (verified destinations), which is meaningful beyond the annotations. It does not describe return format or pagination, which is acceptable given the annotation coverage.

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 a single short phrase that front-loads the resource identity. It contains no wasted words, though the fragmentary structure is slightly less clear than a complete sentence would be.

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 low-complexity read-only tool with one optional parameter, full schema coverage, and rich annotations, the description provides enough domain context to understand what the tool returns. Missing details like explicit list behavior and output format are minor given the simplicity and the tool name.

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%, and the single optional businessId parameter is fully documented in the schema, including its default behavior. The description adds no additional parameter meaning, so the baseline of 3 is appropriate when the schema does all the work.

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 is a noun phrase that identifies the resource as 'Numbers the business proved it controls' and gives examples (allowed test-call targets and ownerPhone). It does not explicitly state the action (list), though the tool name implies it, and it offers some differentiation from list_numbers by scoping to proved/controlled numbers. The missing verb and fragmented phrasing keep it from being a clear verb+resource statement.

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 explicit when-to-use guidance or alternatives are given. The parenthetical examples hint at use cases (test-call targets and ownerPhone), but the description does not say when to prefer this tool over siblings like list_numbers or search_numbers.

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