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 tool's safety is transparent. The description adds critical behavioral details beyond annotations: payment requirement ($0.02/call via x402), the behavior on failed payment (returns 402 with instructions), and the return format (array of fields). No contradictions.

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?

Three concise paragraphs: first states the main function, second provides usage guidance, third covers payment and return format. No redundant sentences, well-organized, and front-loaded with the essential purpose.

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?

Given there is no output schema, the description adequately describes the return format (array of carrier, transit_days, etc.). It also covers payment details and distinguishes from sibling. For a simple two-parameter tool, this is complete and leaves no critical gaps.

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 coverage is 100% with all three parameters described in the input schema. The description does not add significant new meaning about parameters beyond what the schema provides, but it contextualizes the tool's response. Baseline 3 is appropriate as schema does the heavy lifting.

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 verb ('Get'), resource ('estimated ocean transit times'), and scope ('between two ports across all available carriers'). It also distinguishes from the sibling tool 'shippingrates_transit_schedules' by specifying that this is for quick comparison vs detailed routing, establishing a distinct purpose.

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 this tool ('for quick transit time comparison between ports') and when not to use it, directing to an alternative for detailed routing with transhipment ports and service codes ('use shippingrates_transit_schedules instead'). Clear context and exclusion.

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