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

Annotations already cover readOnly and openWorld, but the description adds material context beyond them: pricing ($0.002 USDC per successful call via x402 on Base, Solana or Arc) and the fact that failed calls are not charged. It also discloses the key accuracy caveat that results are estimates, not official tonnage.

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?

Front-loads the computed quantities and their formulas, then appends the accuracy caveat and payment terms. Three dense sentences with no filler, though the formula block is information-heavy and slightly crowds the caveat that matters for correct interpretation.

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?

With an output schema present, return values need not be described, and the description still covers density defaults, the design-stage limitation, and billing behavior. For a 7-parameter calculation tool this is essentially complete, with only the explicit fallback-to-registry path left unstated.

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%, so baseline is 3, but the description adds real meaning by showing how the inputs combine (volume = L × B × T × Cb; displacement = volume × density; deadweight = displacement − lightship) and clarifies what consumablesTonnes produces (remaining cargo capacity). This goes beyond the field-level text in the schema.

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?

States a specific verb and resource (vessel displacement and deadweight estimate from hull dimensions) and spells out the exact formulas, so the agent knows precisely what is computed. It also differentiates from siblings by explicitly excluding registry lookups ('not a vessel's official DWT; no ship registry lookup'), separating it from imo_vessel_dossier and vessel_tracker.

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?

Clearly frames the use case as a design-stage estimate from standard formulas rather than an authoritative registry lookup, which tells the agent when this tool is appropriate. It stops short of naming the sibling tool to use when an official DWT is needed, so routing is implied rather than explicit.

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