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

Annotations already indicate read-only, idempotent, and non-destructive behavior. The description adds useful behavioral warnings about indeterminate results from missing context and that equality does not imply ownership, going 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 brief and front-loaded with the main action, with no redundant filler. The phrase 'after analysis' is slightly unclear but does not significantly harm conciseness.

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 tool has nested objects, optional fields, enums, and a default policy, but the description does not explain the output format, the meaning of 'missing context', or how country codes influence comparison. Important usage context is missing for an agent to call this reliably.

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%, and the description does not explain key parameters like left, right, detail, numberCountryCode, or originCountryCode. It only touches on extensionPolicy behavior, leaving most parameter meanings implicit and requiring inference from names.

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 states the verb 'compare' and the resource 'two numbers', which clearly indicates the core function. It is distinguishable from sibling tools like normalize or analyze, though the phrase 'after analysis' adds slight ambiguity.

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 gives some conditional guidance about extensionPolicy and missing context, but it does not explicitly state when to use this tool versus sibling tools such as analyze_phone_number or normalize_phone_numbers. It implies comparison use cases but lacks direct alternative routing.

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