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

Annotations already declare readOnlyHint=true, so the read-only nature is known. The description adds valuable behavioral context: position data may lag by 30–60 seconds and many fields are null for non-operating vessels, which helps manage expectations about data freshness and completeness.

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 sentences efficiently pack the return payload, usage guidance, and data caveats. The main functionality is front-loaded, and every sentence earns its place.

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 and readOnlyHint annotation, the description covers all essential aspects: what is returned, when to use it, and important caveats about data lag and nulls. No parameters means nothing else needs explaining.

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 0 parameters, so per the rubric the baseline is 4. The description doesn't need to explain parameters, and no additional parameter-related value is required.

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 states a specific verb ('Returns') and resource ('real-time AIS positions, speed, heading, ETA, and dock status for all active WSF vessels'), clearly distinguishing it from sibling tools like ferry schedules or border waits. It also provides concrete use cases ('where is the ferry now?').

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?

The description explicitly says 'Use for' and lists three clear usage scenarios. It does not mention when not to use or alternatives, but since no sibling tool covers vessel location, this is sufficient context without exclusions.

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