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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false, so the safety profile is covered. The description adds useful behavioral context: 5-minute interval granularity, ~2-hour horizon, model version, list of returned variables, geographic coverage, licensing, and 'no auth, no upstream cost' – substantial value beyond the annotations.

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?

Three dense sentences with no wasted words: the action and core facts are front-loaded, followed by return variables, use cases, and licensing. Every sentence earns its 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 two-parameter read-only tool with an output schema, the description covers all necessary context: what it returns, time granularity, coverage, use cases, authentication, and cost. Nothing an agent needs to select and invoke this tool correctly is missing.

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% for both lat and lon, including coverage ranges, so the schema carries the parameter documentation. The description reiterates the coverage bounds and adds no new parameter details, but no additional clarification is needed for these simple coordinate inputs.

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 description states a specific verb ('Get'), a specific resource ('short-term precipitation nowcast with 5-minute intervals for the next ~2 hours'), and names the exact source model (Nowcast 2.0). It also enumerates the returned variables, which clearly distinguishes it from weather.forecast, weather.alerts, and astronomy.sunrise siblings.

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?

The description explicitly identifies ideal use cases: 'hyperlocal outdoor activity planning, event logistics, and real-time rainfall monitoring.' It also provides coverage bounds. It does not explicitly state when to avoid this tool or name alternatives, but the short-term/nowcast framing makes the appropriate context clear.

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