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 behavioral context: the tool is PAID ($0.25/call via x402 with payment instructions if unmet), returns a sorted array, and explains the response format. No contradictions with 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 five sentences with no filler. The first sentence states the core function, the second explains use cases, the third differentiates from a sibling, the fourth covers payment, and the fifth describes the return value. Every sentence earns its place.

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 description covers purpose, usage, payment behavior, alternative tools, and the return format (array of objects with fields, sorted by total_cost). There is no output schema, so the description carries the burden of explaining the response, which it does, though it doesn't elaborate on the 'slabs' field structure or potential error cases. Overall, it's sufficiently complete for a paid comparison tool.

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 100%, so the baseline is 3. The description reinforces the meaning of the three required parameters (country, container type, days) but does not add significant new semantic detail beyond the schema, aside from clarifying that 'days' refers to detention days in the first sentence.

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 the tool's purpose with a specific verb ('Compare') and resource ('demurrage and detention costs across ALL available carriers'), and explicitly distinguishes it from the sibling tool shippingrates_dd_calculate by pointing to that alternative for single-carrier comparisons. This is more than adequate.

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?

Explicitly states when to use: for freight procurement and carrier selection, answering 'which carrier has the cheapest D&D in this country?'. It also directly says to use shippingrates_dd_calculate instead for a single carrier's detailed breakdown, providing a clear when-not scenario.

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