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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuinely useful context beyond that: it warns the agent to preserve source sample dates and unavailable states, clarifies the index is relative rather than measured, and notes the return carries source/freshness metadata.

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?

Front-loaded and compact at three sentences. However, the generic 'Units: ft, kt, s, F, mi; directions FROM' line reads as API-wide boilerplate whose relevance to a clarity index is unclear (knots/Fahrenheit for water clarity), diluting an otherwise tight 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 steps in to say it returns data plus source/freshness metadata, and it flags the relative-index interpretation and unavailable states. That covers the essentials for a single-spot read tool; only minor gaps like error or resolution behavior remain.

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%, so the single 'spot' parameter (with only a pattern/length constraint) is undocumented structurally. The description compensates slightly by qualifying it as a 'verified spot', but gives no format, identifier style, or resolution guidance, so it does not fully close the gap.

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 resource (satellite water clarity) scoped to a 'verified spot', and crucially distinguishes the concept from measured dive visibility, which differentiates it from siblings like get_visibility. It does not name a sibling tool outright, so it falls just short of the top tier.

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?

'For a verified spot' implies the precondition that the spot must exist/be verified, and the caveat that this is a relative index hints at when it is and isn't appropriate. However, there is no explicit when-to-use/when-not or pointer to the alternative (e.g. get_visibility for actual dive visibility), leaving usage largely implied.

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