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

Annotations already declare readOnlyHint/idempotentHint/destructiveHint=false, so the safety profile is covered. The description adds genuinely non-structured context: the BYO-token requirement and where to get it, plus the semantic meaning of 'gap' as AIS transmission being switched off. It omits pagination/rate-limit behavior, but that is documented in the offset parameter.

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?

Four tight sentences: scope, taxonomy, payload shape, auth requirement. The resource and date-range scoping are front-loaded, and nothing is repeated from the schema verbatim.

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?

There is no output schema, so the description compensates by stating that each event carries position, start/end time, and involved vessels — enough for an agent to know what comes back. With required params, paging, and auth all covered across description and schema, nothing material is missing.

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 the baseline is 3. The description earns above baseline by explaining what each event type actually means (encounter = vessels meeting at sea, gap = transmission switched off) and by restating the _apiKey auth requirement, both of which add interpretation the enum-less schema string does not provide.

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 ('Global Fishing Watch vessel events over a date range') and then enumerates the exact event taxonomy — fishing, encounter, loitering, port_visit, gap — before describing the payload. An agent can immediately tell this returns event records rather than vessel metadata, distinguishing it from the sibling gfwfish_vessels_search.

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 three quoted questions ('where was this vessel fishing', 'did it meet another vessel at sea', 'did it go dark') give concrete use-case triggers that map cleanly onto the event types. It stops short of explicit exclusions or routing — e.g. it never says in the description to call gfwfish_vessels_search first to obtain a vessel_id, which only appears buried in the schema.

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