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

Annotations already declare readOnlyHint=true, destructiveHint=false, and idempotentHint=true. The description adds valuable behavioral context beyond those: payment is required ($0.02/call via x402), failure returns 402 with payment instructions, and the return format is explicitly stated as an array of surcharge objects. This extra information provides practical operational transparency without contradicting any 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 well-organized and front-loaded: it starts with the core action, lists examples, gives the use case, explains the context, provides an alternative, and ends with payment and return details. Every sentence carries distinct information, and the text is appropriately sized for the tool's complexity.

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?

Despite no output schema, the description explicitly defines the return structure (array of objects with specific fields). It also covers payment prerequisites, error behavior, and the relationship to base freight rates. For a tool with 4 params and 100% schema coverage, this description is fully sufficient for an agent to select and invoke it correctly.

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 does not add significant parameter-level detail; it only mirrors the schema concepts (carrier, country, direction). It does not explain syntax, defaults, or constraints beyond what the schema already provides. Thus the description adds minimal semantic value over the structured schema.

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 opens with 'Get carrier-specific surcharges', a specific verb+resource combination. It enumerates concrete surcharge types (BAF, CAF, PSS, EBS) and clearly distinguishes from sibling tools by focusing on surcharges rather than base rates or total cost. The explicit mention of shippingrates_total_cost as an alternative further sharpens the tool's unique role.

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 directly states when to use the tool: 'Use this to understand surcharge exposure for a carrier in a specific country/direction.' It also provides an explicit alternative: 'For a complete cost breakdown, use shippingrates_total_cost which includes surcharges automatically.' This gives clear decision guidance relative to siblings.

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