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

With no annotations, the description fully discloses the behavior: it places one short call, speaks a 6-digit code twice, hangs up, and requires confirmation within ten minutes. It also explains the no-op behavior for already-verified numbers and the rate limits, leaving no hidden surprises.

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 four sentences, every one of which adds value: purpose, behavior, next step, and limitations. It is front-loaded with the most important information and avoids 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 single-parameter tool with no annotations or output schema, the description is remarkably complete. It covers prerequisites, the call process, timeout, next steps, and rate limits, making it sufficient for an agent to invoke and handle the flow 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 coverage is 100% for the single parameter 'number', with a clear E.164 format example. The description does not add extra parameter semantics beyond this, so the baseline of 3 is appropriate.

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 ('Prove your account controls a phone number') and clearly identifies the resource (a phone number) and the context (before any PSTN test call). It distinguishes itself from siblings by naming verify_number_confirm and stating 'This is the only action that dials an unverified number.'

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 explicitly states when to use this tool ('before any PSTN test call'), what to do next (confirm with verify_number_confirm), and even notes that calling an already-verified number places no call. It also clarifies the tight call caps, providing clear guidance on usage limits.

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