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

Annotations already declare readOnlyHint and openWorldHint, but the description adds substantial behavioral context beyond them: the paid x402 pricing model, accepted payment chains, and the fact that failed calls are not charged. It also discloses the geographic limitation that causes empty results, which is valuable operational context not present in annotations.

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?

Two dense sentences with zero waste. The core capability and scope are front-loaded, followed by the critical coverage limitation and pricing, all in a compact structure.

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?

An output schema exists, so return values need not be explained. The description covers what the tool returns (position, speed, heading, voyage status), the data source, coverage limits, and payment behavior—everything an agent needs to decide and invoke 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%, and the single parameter already documents the 9-digit MMSI format with an example. The description reinforces '9-digit MMSI' but adds no meaningful syntax or semantic detail beyond what the schema provides, so the baseline of 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: live AIS position, speed, heading and voyage status for one vessel by MMSI, and names the data source (Finland's Digitraffic AIS feed). This clearly distinguishes it from sibling tools like logistics_imo_vessel_dossier or logistics_dark_fleet_ais_gap.

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 the coverage boundary: 'Covers Finnish and Baltic waters only, not global coverage; vessels outside that area return no position.' This gives a clear when-not condition, though it does not name specific alternative sibling tools for global AIS coverage.

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