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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds genuine domain context beyond that: the lifecycle vocabulary (buying, owned, unpaid, releasing) and the rule that toll-free verification must be approved before a number can send. The trailing 'Read only' merely restates the annotation, a minor redundancy rather than an error.

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?

A single front-loaded sentence identifies the resource immediately, followed by the return contents. The clause 'which must be approved before the number can send' is slightly tangled but earns its place by explaining the verification field's consequence.

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 zero parameters, the description needn't document return shape or inputs, and it correctly focuses on domain semantics of the returned states. The only gap is the lack of any pointer to sibling tools for filtered or single-number lookups.

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?

The tool takes zero parameters, so the baseline is 4; there is nothing for the description to clarify about inputs. It instead spends its words on the meaning of returned fields, which is appropriate for a no-arg list call.

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 clear resource ('The account's business numbers ... US toll-free numbers bought from Sparetext') and enumerates what is returned (state plus toll-free verification). It doesn't explicitly differentiate itself from siblings like search_numbers, get_number, or request_business_number, so an agent must infer that this is the unfiltered full enumeration.

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?

Usage is only implied by the verb 'list' and the 'Read only' note; there is no statement of when to prefer this over search_numbers (filtering) or get_number (single lookup). An agent can guess the intent, but no explicit routing guidance or exclusions are given.

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