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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so the safety profile is covered. The description's genuine addition is the pricing note "(Cost: 2 credits)", which is useful context an agent cannot get from annotations. It does not disclose accuracy limits at coastlines, boundary conventions, or how ambiguous points (rivers, lakes, piers) are treated.

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 opening redundantly repeats the tool name twice ("Coordinates Are Sea: Coordinates Are Sea checks...") and the third clause restates the boolean result already implied by the first sentence. It is short overall, but two of its three sentences do not earn their 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?

For a low-complexity two-parameter predicate with an output schema, full schema coverage, and read-only annotations, the description supplies everything essential plus cost. The only shortfall is the absence of any note on coastline/boundary edge cases, which matters for a land-vs-sea classifier.

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% and both parameters are documented with types and examples, so the schema carries the burden. The description only restates that a latitude/longitude pair is passed, adding no format, range, or precision guidance beyond the schema. Baseline 3 is appropriate.

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?

"checks whether a given latitude and longitude pair sits in the ocean or on land" states a specific verb (checks) and resource (lat/lon pair) with a clear boolean outcome. It is unambiguous against most siblings, though it never names a related tool (ReverseGeocode, CountryBoundaries, MarineWeather) that an agent might confuse it with.

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?

Usage is only implied by the purpose statement: an agent can infer "use this when you need land/sea classification for a point," but there is no explicit when-to-use, no exclusion, and no mention of when a reverse geocoder would be the better choice. No prerequisites or input constraints are given.

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