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

Adds context beyond annotations: nothing is reserved or charged here, and the human-in-the-loop requirement ('Show the user... let THEM pick'). The return shape is described inline, which the annotations do not cover.

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?

Front-loaded with the purpose and use condition, then return shape, then the next step. Dense and mostly earned, though the final sentence on the user's own number lengthens it slightly.

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?

No output schema exists, and the description explains the return fields ({ numbers, monthly_price_cents, purchasable, instructions }) and number locality. An agent has everything needed to call correctly and route the follow-up.

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%, so the schema already documents all five parameters including the country guidance. The description adds no parameter-level detail beyond what the schema provides; baseline 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?

Specific verb+resource ('Find phone numbers the user can rent from DripRaven') with the purpose (WhatsApp registration) stated. It is clearly distinguishable from siblings list_phone_numbers (existing numbers) and buy_phone_number (purchase).

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?

Explicit trigger condition (user has no spare number and the Meta number cannot already be on WhatsApp), an alternative path (use the user's own number — cheaper and more reliable), and the follow-up action (buy_phone_number). Nothing 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.