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

Annotations already cover readOnly, idempotent, and non-destructive traits. The description adds value by disclosing that the tool is free ('FREE — no payment required') and clarifying the scoped nature of the data (reviewed shipping lines with live D&D coverage), which goes 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 concise and well-structured: first sentence states the core function, second gives usage context, third notes the free aspect, fourth specifies the return format, and fifth points to related tools. Every sentence earns its place without redundancy.

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 zero-parameter, read-only listing tool, the description is complete. It covers what it lists, why you'd use it, the cost (free), the return structure, and relationships to sibling tools. There is no output schema, but the description fills that gap by explicitly naming the return fields.

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 tool has zero parameters, so the baseline is 4. The description correctly explains what is returned (Array of { shipping_line, country, records }), which provides semantic meaning for the tool's output without needing parameter details.

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 a specific verb ('List') and a specific resource ('reviewed shipping-line identities that currently have live D&D coverage, with per-country record counts'). It distinguishes itself from sibling tools by explicitly mentioning alternatives for aggregate totals and keyword-based discovery.

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 provides explicit when-to-use guidance ('Use this to discover which carrier-country D&D combinations are currently available before querying a tariff tool') and names related tools (shippingrates_stats, shippingrates_search), giving clear context for when not to use this tool.

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