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

With no annotations provided, the description carries the full burden and delivers substantial behavioral disclosure: the operator is a DETECTED guess from the number range, MVNOs resolve to their host network, and buying a voucher for the wrong network delivers successfully but cannot be redeemed or refunded. It also mentions the correction path via other_brands and that the tool is free, which are material beyond the schema.

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 front-loaded with the core purpose, then concisely adds the free status, the detection caveat, and the critical purchase-confirmation workflow. Every sentence carries distinct information with no filler or repetition.

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?

The description covers purpose, uncertainty of operator detection, the need for human confirmation, correction via other_brands, and the failure mode of a wrong-network purchase. It does not describe the structure of the returned top-up offers or how other_brands appears in the response, but the operational guidance is strong for a tool with no output schema.

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 single parameter is already fully documented in the schema as an E.164 phone string with an example, so the description does not need to duplicate that. The description adds context about the purpose of the phone number but no additional constraints, formats, or parameter-specific guidance.

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 identifies the country and mobile operator of a phone number and lists top-up offers, which goes well beyond the tool name. It does not explicitly differentiate itself from the sibling tool list_offers, so sibling distinction is incomplete.

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 establishes a clear pre-purchase workflow by instructing the agent to read the detected brand back to the human and have it confirmed before buying. However, it does not explicitly state when to use this tool over list_offers or other siblings, leaving the tool-selection context implicit.

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