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 agent knows this is a safe read. The description adds valuable behavioral context beyond annotations: the payment requirement ($0.05/call via x402) and the 402 error response without payment. It also discloses the return fields, making the tool's behavior more predictable. Missing only minor details like pagination or rate limits, but it's well-covered.

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 compact and front-loaded: purpose first, then use case, then alternatives, then payment, and finally return format. Every sentence earns its place, with no redundant filler. It's long enough to be useful without being verbose.

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 rate-lookup tool with 8 parameters (2 required) and no output schema, the description delivers a complete picture: it explains when to use, what it returns (including the full array structure), payment requirements, and alternatives. Combined with the rich schema annotations, the agent has everything needed to select and invoke this tool 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 each parameter has a description with examples and enums. The tool description doesn't add much parameter-level meaning beyond what the schema provides, but it does contextualize x_payment by explaining the payment mechanism and failure mode. That's marginal added value, so baseline 3 is appropriate.

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+resource: 'Get inland haulage (trucking/rail) rates for moving containers between a port and an inland location.' It clearly distinguishes itself from siblings by explicitly pointing to shippingrates_inland_search for exploring routes and shippingrates_inland_compare for carrier comparison, making the tool's unique purpose obvious.

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?

Provides explicit usage guidance: 'Use this when you know the specific origin port and destination and need rate quotes.' It also tells the agent what to use instead for route discovery and rate comparison, effectively stating when not to use this tool. This is exactly the kind of decision support needed.

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