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

Annotations already declare readOnlyHint and openWorldHint, but the description adds genuinely new behavioral facts: a metered price of $0.002 USDC per successful call, x402 payment on Base/Solana/Arc, and the guarantee that failed calls are not charged. Data provenance (AIS-derived) and the coverage limitation further reduce surprise; a 5 would need more on freshness or latency.

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?

Three sentences, all front-loaded: capability first, then scope exclusions, then cost/payment. Pricing is not padding here because a paid call affects whether an agent should invoke it.

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 no explanation. Source, coverage boundary, and payment/cost terms are all covered, which is everything an agent needs before spending $0.002 on a call.

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?

Only one optional parameter and schema coverage is 100%, so the schema already documents the 1–30 day range and default. The description adds only an implicit notion of daily granularity ('Daily vessel transits'), 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?

States a specific verb and resource (daily vessel transits through the Bosporus, counted by ship type with capacity) plus the upstream source (IMF PortWatch, AIS-derived). It also explicitly carves out what it is not — Bosporus only, not the Dardanelles — which separates it from canal/strait siblings at a glance.

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?

Gives clear scope boundaries: Bosporus only, excludes the Dardanelles, and does not provide waiting times, so an agent knows what questions it cannot answer here. It stops short of naming a named alternative tool for Dardanelles or waiting-time data, which keeps it from a 5.

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