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

Annotations cover safety (readOnly, openWorld, non-destructive), so the bar is lower, yet the description adds substantial context: AIS is a last-known fix not a live feed, terrestrial coverage gaps make outdated fixes normal, freshness bucket thresholds, and the trap that position_updated_at is not the fix age.

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?

Longer than typical, but front-loaded with purpose and every sentence guards against a specific misinterpretation (freshness semantics, coverage gaps, the updated_at trap). Dense but not padded; the impartial reading is that it earns its length.

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?

For a one-param read tool with an output schema, nothing needed is missing: the input source, the interpretation of freshness fields, and the caveat about what the position does and does not mean are all stated.

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% for the single `imo` parameter, so the baseline is 3. The description adds value by specifying where the IMO comes from (get_container_detail), though it doesn't add format detail beyond the schema's example.

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+resource (last known AIS position for a vessel) and enumerates the returned fields. It is clearly distinguishable from siblings like get_container_detail, which it cross-references for input.

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 the prerequisite input source (IMO from get_container_detail) and explicit when-to-use / how-not-to-use guidance: report the age, never present an outdated fix as current location. This routes behavior, not just retrieval.

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