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

Beyond the readOnly/openWorld annotations, the description discloses the data source, the restricted composite-only extraction scope, the per-call price, accepted payment rails, and that failed calls are not charged. This is unusually strong behavioral context for a zero-parameter data tool.

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 data product, then gives the important scope limitation, then the pricing model. Every sentence adds useful information with no filler.

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 a zero-parameter tool with an output schema already defined, the description covers source, scope, return contents at a high level, pricing, and failure charging. An agent has enough information to invoke it 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?

The tool has zero input parameters, so parameter semantics are inherently limited and the baseline is 4. The description instead clarifies the returned data fields and extraction boundary, but there are no input parameters to explain.

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 names a specific data product (Drewry WCI composite spot rate per 40ft container) and specifies that it returns the weekly date and change. It also narrows scope by excluding route-level Shanghai-Rotterdam and Shanghai-Los Angeles values, though it does not explicitly contrast itself with named sibling tools.

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?

Usage is implied by the scope statement: this is for the composite WCI rate, and route-level values are explicitly not extracted. However, there is no explicit guidance on when to choose this tool over related freight-rate or logistics tools.

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