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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds valuable context beyond annotations: 'FREE — no payment required', 'reviewed' (trusted data), 'live D&D coverage' (current availability), and the exact return structure. It does not contradict any annotation.

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 compact and well-organized: a clear first sentence for the main action, a short usage sentence, a cost note, the return type, and related tools. Every sentence serves a purpose with no redundancy or fluff.

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 list tool, the description covers all necessary context: purpose, use case, cost, return format, and related alternatives. It is self-contained despite the absence of an output schema, and the sibling tool landscape is addressed via explicit pointers.

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 input schema has zero parameters, so the baseline is 4. No parameter explanations are needed. The description instead clarifies the output meaning (shipping_line, country, records), which is useful given no output schema exists.

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 a specific verb ('List') and resource ('reviewed shipping-line identities'), with qualifiers ('currently have live D&D coverage', 'per-country record counts') that precisely define scope. It distinguishes from siblings by explicitly framing this as a discovery step before querying a tariff tool.

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 says 'Use this to discover which carrier-country D&D combinations are currently available before querying a tariff tool' and explicitly names alternatives: 'Use shippingrates_stats for aggregate totals, shippingrates_search for keyword-based discovery.' This provides clear when-to-use and when-not-to-use guidance.

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