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

Annotations already flag destructiveHint and idempotentHint, but the description goes well beyond them: billing stops immediately, the release is permanent, and if it is the WhatsApp-connected number that connection breaks and re-registration is required. It even discloses the return shape ({ phone_number, released, instructions }), which no output schema provides.

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?

Four sentences, each carrying distinct load: action, triggers, confirmation guardrail, consequences/return. The irreversible effect is front-loaded in sentence one and reinforced before the call.

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 destructive tool with no output schema, the description supplies everything an agent needs: irreversible effect, downstream WhatsApp impact, a confirmation requirement, and the return shape. No material gaps remain.

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 already documents that phone_number accepts E.164 or an id from list_phone_numbers. The description only refers to 'the number' generically, adding no format or sourcing detail beyond the schema, so the baseline of 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?

States a specific verb+resource ('Give a rented phone number back') plus the billing side effect, which immediately distinguishes it from buy_phone_number and list_phone_numbers. An agent can tell what this does without opening the schema.

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?

Names two concrete triggering conditions ('user no longer wants the number', 'WhatsApp would not accept it') and adds an explicit precondition: confirm with the user before calling. Nothing about when to invoke it is left to inference.

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