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

Annotations already declare readOnly, openWorld, idempotent, and non-destructive, so the safety profile is covered. The description does add genuinely useful behavior: explicit nulls when unavailable, timestamp and source/freshness metadata. But it also leaks irrelevant unit details (water temperature F, current sign) and never states the rain accumulation unit, which is a notable omission for a rain tool.

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 first sentence is well front-loaded, but the remainder is a pasted block of unit conventions covering water temperature, visibility, and currents that do not apply to rain. Those sentences do not earn their place and dilute the signal for the actual tool.

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 mention timestamp, source status, null handling, and freshness metadata, which is solid. It still omits the rain accumulation unit and the hours bounds, and the irrelevant unit list makes the picture less complete rather than more.

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% for a nested query object with spot and hours, so the description must compensate. 'Verified spot' is a useful constraint the schema doesn't express, but hours (default 24, max 168) is only gestured at via 'over the next hours', and the spot pattern/verification mechanism is never explained. Partial compensation at best.

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?

The opening sentence gives a specific verb and resource ('Rain probability and accumulation... over the next hours') and scopes it to a verified spot, which is clear enough to separate it from sibling weather tools. However, the body immediately drifts into water temperature, atmospheric visibility, and current sign conventions, which are properties of other tools, not rain. That off-topic content muddies an otherwise clean purpose statement.

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 a weak temporal hint ('over the next hours'), but no explicit when-to-use, when-not-to-use, or alternative routing against siblings like get_forecast, get_conditions, or get_thunder_forecast. An agent gets no guidance on when rain deserves its own call versus a general forecast call.

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