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

Annotations already declare read-only, idempotent, non-destructive behavior, but the description adds substantial context beyond them: quotes expire in 30 minutes, the search is free, and results are constrained by carrier identity-document requirements and per-minute cost thresholds for bots. It also explains that countries outside the US/Canada return reasons when no numbers qualify, which sets expectations for empty or filtered results.

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 definition is front-loaded with the core value proposition and next-step guidance, and every sentence carries useful information about pricing, quote expiry, or eligibility. The fragment 'Free.' at the end is terse but still meaningful; otherwise the structure is efficient.

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 no output schema, the description gives enough behavioral context for an agent to call this correctly and understand the result lifecycle: rental price included, free to search, quote validity, and eligibility reasons. It does not describe pagination, result limits, or exact output shape, which are minor gaps for a discovery tool.

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 schema has 75% description coverage, so city, country, and area_code are largely documented there, and type is a simple enum with a default. The description does not add meaning to any individual parameter, but the high schema coverage makes 3 the appropriate baseline.

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 and resource: finding phone numbers the business can rent right now, with their monthly price. It clearly distinguishes discovery from the sibling phone_list_numbers (existing numbers) by focusing on rentable inventory, and from phone_rent_number by making this the search 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?

It explicitly tells the agent the next step—pass the quote to phone_rent_number—and warns that quotes last 30 minutes, which is crucial usage context. It also scopes what kinds of numbers are usable by bots (no identity documents, under $0.25/minute). It stops short of explicitly stating when to prefer phone_list_numbers, so it is not a full 5.

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