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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds genuinely non-obvious behavior: a nearest-buoy preference within a 40 km radius with silent fallback to satellite data, which tells the agent the result is a point estimate with resolution limits. It omits units, update cadence, and whether the fallback is surfaced in the response.

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?

One sentence, front-loaded with the primary data source and the fallback condition immediately after; nothing is redundant with the title or the schema.

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 simple two-parameter read tool with annotations covering safety and openness, the description is close to sufficient. But with no output schema, it leaves the return contract unclear — units (Celsius/Fahrenheit), whether a timestamp or station identifier is returned, and how nulls over land are handled are all unstated.

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% and both parameters carry WGS84 documentation, so the schema does the heavy lifting (baseline 3). The description adds only implicit meaning about how lat/lng are used (proximity search radius of 40 km), which sets precision expectations but adds no syntax or format detail.

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?

Names a specific resource (water temperature / sea surface temperature) and, unusually, states the data source policy, so an agent understands what value it is actually getting. It does not, however, differentiate itself from nearby siblings such as `currents` or `marine_forecast`, which an agent may reasonably consider for the same coordinate.

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 or when-not-to-use guidance, no mention of alternatives among the many marine siblings, and no stated prerequisites or coordinate-domain constraints. The agent must infer that this is the right tool simply because the name matches the topic.

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