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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description adds useful behavioral context beyond annotations: it returns id_operator and id_country for downstream steps and tells the agent to ask the user on failure.

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 four short sentences with no wasted text. The primary instruction to call it first for phone-number top-ups 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?

An output schema exists, so the description does not need to fully explain return values, though it helpfully names id_operator and id_country. The only meaningful gap is that lang is not explained anywhere, despite being an enum parameter.

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 required phone parameter is documented in the schema with E.164 format and an example, and the description reinforces that format. However, the lang parameter is an enum with no description in the schema or the tool description, leaving half the parameters undocumented.

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 uses a specific verb and resource: identify the mobile carrier and country from a phone number. It also distinguishes this lookup from sibling listing tools like get_operators and get_countries by tying it directly to a phone-number input and top-up flow.

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 gives explicit sequencing guidance: ALWAYS call this FIRST when the user provides a phone number for a top-up. It also specifies a fallback action if lookup fails, asking the user which carrier/network the number uses.

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