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

Beyond the readOnly/idempotent annotations, the description discloses the payment requirement (PAID $0.02/call via x402), the failure behavior (returns 402 without payment), and the return shape. This is valuable behavioral context that annotations do not cover.

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 front-loaded with the core purpose, followed by usage guidance, sibling distinction, payment details, and return format. Every sentence contributes necessary information without redundancy or fluff.

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?

For a simple two-required-parameter lookup tool with no output schema, the description is complete: it covers the function, usage boundaries, payment requirements, return format, and alternative tool. No important context is missing.

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 has 100% coverage with clear descriptions and examples for origin and destination, so the baseline is 3. The tool description does not add per-parameter details beyond what the schema already provides, though it does frame the parameters as 'between two ports'.

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 a specific verb and resource: 'Get estimated ocean transit times between two ports across all available carriers.' It clearly distinguishes itself from the sibling tool shippingrates_transit_schedules by noting that this is for quick comparison while the sibling handles detailed routing with transhipment ports and service codes.

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 the tool ('quick transit time comparison between ports') and names the alternative for more detailed needs ('use shippingrates_transit_schedules instead'). This gives the agent clear decision-making guidance.

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