set_phone_number_allow_list

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

No annotations are provided, so the description carries the full burden. It states that the tool replaces the existing allow list and that an empty list clears it. However, it does not disclose behavior such as idempotence, error handling for invalid IDs or numbers, or permissions requirements. This is adequate but not richly transparent.

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 extremely concise: three sentences. The first sentence states the primary purpose, the second explains the replacement behavior, and the third details parameters. There is no superfluous information, and the most important detail (clear functionality) is front-loaded.

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 setter tool with two required parameters and an existing output schema, the description covers the core functionality and parameter semantics. It does not explain return values, but with an output schema present, that is acceptable. It lacks discussion of error cases or side effects, but overall it is reasonably complete.

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?

With 0% schema description coverage, the description compensates well. It defines phone_number_id as 'The phone number ID (from list_phone_numbers)' and numbers as 'List of E.164 phone numbers to allow, e.g. ["+15551234567"]'. This adds substantial meaning beyond the schema's bare types.

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 verb 'Set' and the resource 'allow list for a phone number'. It distinguishes from the sibling tool 'set_phone_number_block_list' by explicitly stating the allow list controls who can send SMS. The parenthetical '(only these numbers can send SMS to it)' further clarifies the purpose.

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 explains when to use the tool (to set or update the allow list) and how to clear it by passing an empty list. It also tells where to obtain the phone_number_id (from list_phone_numbers). While it does not explicitly say when not to use it, the context of sibling tools implies alternatives like block list. The guidance is clear for the intended use case.

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