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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds essential non-obvious behavior: the payment requirement ('PAID: $0.03/call via x402') and the 402 response without payment. It also discloses the return structure. This goes beyond annotations but is not exhaustive (e.g., no rate limits or pagination behavior), so a 4 is appropriate.

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 (about 70 words) and well-structured: purpose sentence, usage guidance, payment note, and return format. Every sentence earns its place, and the most important information (purpose and when to use) is front-loaded. No fluff or redundancy.

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 the tool's complexity (5 params, no output schema), the description fully covers purpose, usage differentiation, payment constraint, and return structure. The agent has all necessary context to decide when to call and what to expect. The absence of an output schema is compensated by the explicit return array description.

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 new parameter-level detail beyond the schema; it mentions the purpose of routing details but does not elaborate on how to format parameters (e.g., UN/LOCODE format is already in schema). The description does hint at return fields but not parameter semantics.

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 detailed transit schedules for a specific carrier' — a specific verb and resource. It enumerates the exact data returned (service codes, transhipment ports, transit days, frequency) and explicitly distinguishes itself from the sibling tool shippingrates_transit by stating it provides routing details beyond transit time.

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 explicitly states when to use this tool: 'Use this when you need routing details beyond just transit time...'. It also names the alternative: 'For a quick transit time comparison across all carriers, use shippingrates_transit instead.' This clear guidance leaves no ambiguity.

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