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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), and the description adds real value beyond that: explicit nulls when data is unavailable, inclusion of source/freshness metadata, and the unit conventions for returned values. It still doesn't say what happens with an unverified spot or how stale data is flagged.

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?

The purpose is front-loaded in the first sentence, which is good. However, the clause about atmospheric visibility vs underwater visibility and the current sign convention are tangential for a water-temperature tool and read as noise, diluting an otherwise compact description.

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 no output schema, the description carries the return-value burden and does so reasonably: timestamp, source status, explicit nulls, units, and freshness metadata are all disclosed. What is missing is guidance on unverified spots and how the 'hours' window behaves at its bounds.

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 0% on a nested query object, so the description must compensate. It clarifies that 'spot' must be a verified spot and that 'hours' is a forecast horizon, but gives no detail on valid spot formats or the 1-168 hour range, leaving half the semantic burden on the schema's raw constraints.

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 ('Water temperature') and scopes it to a verified spot over the next hours, which lets an agent separate it from get_air_temperature and get_wind without opening schemas. It does not explicitly name a sibling, so it falls short of a 5.

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?

There is no when-to-use guidance, no mention of alternatives (e.g. get_air_temperature, get_conditions), and no prerequisites beyond the implicit 'verified spot'. The agent must infer usage from the name alone.

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