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

Annotations already declare the tool as read-only, idempotent, and non-destructive, so the safety profile is covered. The description adds valuable behavioral context: it clarifies that results are 'numbering assignments' and explicitly excludes current location and carrier. This tells the agent that the tool does not perform real-time geolocation, which is a meaningful behavioral disclosure beyond the annotations.

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 two sentences long and wastes no words. It front-loads the primary action and then immediately adds the key limitation. Every sentence earns its place: the first states what the tool does, the second clarifies what it does not, both essential for correct invocation. The structure is efficient and clear.

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 return-value details are not required. However, with 0% parameter coverage, the description leaves the agent without any understanding of how the optional parameters alter behavior. The tool is not trivial—it has four parameters and returns candidate objects—and the description does not explain the meaning of 'metadata-backed' or the role of country codes. This incompleteness could lead to misconfiguration, especially since 'originCountryCode' has no obvious purpose from the description alone.

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?

Schema description coverage is 0%, meaning the schema itself provides no descriptions for the parameters. The description offers zero information about what 'detail', 'numberCountryCode', or 'originCountryCode' mean or how they affect the result. Since the schema is the only other source and it lacks explanations, the description completely fails to compensate. An agent would have to guess the semantics of these optional parameters, which is a significant gap.

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 ('Resolve') and a clear resource ('phone number to metadata-backed country candidates or non-geographic numbering'). It also explicitly states what the tool does NOT do (current location or carrier), which sharply distinguishes it from sibling tools like analyze_phone_number or get_phone_capabilities. This leaves no ambiguity about the tool's core 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 implies usage: use this tool when you need country candidates based on numbering plan metadata. It also provides a negative guidance (not location/carrier) that helps avoid misuse. However, it does not explicitly name alternative tools or state conditions like 'use analyze_phone_number for deeper analysis' or 'use lookup_country_calling_code for a single code'. The guidance is clear but not prescriptive about when to choose this over siblings.

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