List phone-verification services

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

With no annotations, the description carries the full burden. It clearly indicates this is a read-only listing operation by using the verb 'List' and further adds value by mentioning that prices are included. It does not explicitly state that no rental occurs, but the contrast with sibling tools makes this sufficiently clear.

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 a single, well-structured sentence that front-loads the core purpose, provides concrete examples, and mentions prices. There is no wasted wording; every element earns its place.

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 simple, parameterless list tool with no output schema, the description is complete. It tells the user exactly what will be returned (services and prices) and gives illustrative examples, leaving no critical gaps for the intended use case.

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 tool has zero parameters, so the baseline is 4. The description needs to add no parameter meaning, and it appropriately focuses on the output (list of services and prices). The schema coverage is trivially 100% since there are no properties.

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 clearly states the tool's purpose with a specific verb ('List') and resource ('services a real UK phone number can be rented for'), and includes examples (WhatsApp, Telegram, Google, Discord) to eliminate ambiguity. It distinguishes itself from sibling tools like rent_test_phone_number by focusing on the listing aspect rather than the rental action.

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 provides clear context—this is for seeing available services and prices before renting a UK phone number—which implies when to use it. However, it does not explicitly state exclusionary guidance (e.g., 'use rent_test_phone_number to actually rent') or mention a specific alternative tool, so it falls short of a 5.

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