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

Annotations already indicate readOnly and idempotent. The description adds the paid nature ($0.05/call via x402) and the 402 error without payment, which is not in annotations. It also discloses the return format (array of charge objects), adding useful behavioral context beyond the structured fields.

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 well-structured with clear line breaks: purpose, usage, payment, and return format. Every sentence earns its place, with no redundant content. It is front-loaded with the primary purpose and efficiently conveys all necessary information.

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, and return format. However, the optionality of port_code is not clarified in the description: it says 'at a port' but port_code is not required, leaving ambiguity whether results are for a specific port or all ports in a country. This minor gap prevents a perfect score.

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% with each parameter already described. The tool description itself does not add parameter-level meaning beyond what the schema provides, so it earns the baseline of 3 without needing compensation.

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 it 'Get local charges at a port for a specific carrier' with concrete examples (THC, documentation fees, seal fees). It distinguishes itself from siblings by explicitly mentioning complementary tools (dd_calculate, total_cost) and focusing on port-specific charges rather than broader shipping costs.

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?

Provides explicit 'when to use' guidance: 'when calculating total shipping costs at origin or destination.' It also names alternatives and how to combine: 'Combine with shippingrates_dd_calculate for a complete port cost picture, or use shippingrates_total_cost for an all-in-one landed cost estimate.' This gives clear decision support.

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