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

The annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds valuable context beyond these: the paid nature ($0.01/call via x402), the 402 response without payment, and the exact return object shape. 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 concise and well-structured with four purposeful sentences. It front-loads the core purpose, then adds usage guidance, payment terms, and return format. No filler or redundancy; every sentence carries 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?

Despite no output schema, the description explicitly documents the return fields, making the contract complete. It covers what the tool does, when to use it, the payment and error behavior, and the data shape. Given the low complexity (1 required param), this is fully sufficient.

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 covers both parameters well (100% coverage), including examples for 'code' and a description for 'x_payment'. The description adds context by explaining the payment requirement ('PAID: $0.01/call via x402... Without payment, returns 402') and clarifies that 'code' is an UN/LOCODE, reinforcing schema examples. This elevates it slightly above the baseline.

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 uses a specific verb 'Look up' with a specific resource ('port details by UN/LOCODE') and lists concrete fields (name, country, coordinates, timezone, terminal facilities). It clearly distinguishes itself from sibling tools by scoping to LOCODE lookups and explicitly directing unknown-code searches to shippingrates_search.

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 explicitly states when to use the tool ('validate port codes or get port metadata') and provides a clear alternative: 'If you don't know the UN/LOCODE, use shippingrates_search with the port or city name first.' This is direct, actionable guidance for tool selection.

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