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

No annotations are provided, so the description carries full responsibility. It discloses key behaviors: code is single-use, expires after ten minutes, and locks after five incorrect attempts, plus the successful outcome (number becomes a permitted PSTN test destination). This provides substantive behavioral context beyond just the operation.

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 concise sentences with no unnecessary words. The description front-loads the action and mechanism, then states the outcome and important constraints. Efficient and well-structured.

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?

The description adequately covers the tool's purpose, workflow position, and safety constraints. Since there is no output schema, the description doesn't describe return values, but the key effect (number becomes permitted) is stated. A minor gap remains regarding response format, but overall complete for the tool's simplicity.

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 input schema already describes all parameters at 100% coverage, so the baseline is 3. However, the description adds critical context for the 'code' parameter: it is spoken on the call and has lifecycle constraints (single-use, expiry, lockout). This enrichment justifies a 4.

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 ('Finish verifying') with a clear resource ('phone number') and mechanism ('6-digit code'), and distinguishes itself from sibling tool verify_number_start by indicating this is the completion step.

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 'Finish verifying' phrasing clearly implies this is the second step after verify_number_start, providing context for when to use it. However, it doesn't explicitly name the alternative or state when not to use it, so it misses the 'explicit when/when-not' threshold for a 5.

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