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

Annotations already declare readOnlyHint, openWorldHint, and idempotentHint, covering the safety profile. The description adds valuable behavioral context: it specifies the output includes observed values and forecast series, and provides a Kp-to-G-scale and aurora-latitude mapping to help interpret results. It does not cover rate limits or auth, but with annotations covering safety, this is sufficient.

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 sentences, the first front-loads the core function and output. The second sentence explains the Kp scale thresholds and aurora correlations, which is informative but arguably background knowledge. The third sentence provides routing to an alternative. Each sentence earns its place, though the scale explanation could be considered slightly tangential. Overall well-structured and not overly verbose.

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 tool with one optional parameter and an existing output schema, the description is complete. It covers what is returned (observed and forecast series), how to interpret it (G-scale mapping, aurora latitude), and when to use it vs an alternative. The output schema documents the exact structure, so nothing essential 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%: the single parameter window_days has a full description in the schema, including range and purpose. The tool description does not mention the parameter at all, which is acceptable given the high schema coverage. The baseline of 3 applies, and the description adds no additional parameter semantics beyond what the schema already provides.

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 clearly states it returns recent observed 3-hour Kp values with NOAA G-scale equivalents and aurora-latitude guidance, plus a 3-day forecast series. It also explains the Kp index scale and its significance, and explicitly differentiates from the sibling tool noaa_spaceweather_get_conditions by stating which tool to use for a combined snapshot. The verb+resource is specific and unambiguous.

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?

It explicitly names the alternative tool (noaa_spaceweather_get_conditions) and provides a clear selection criterion: use the conditions tool for a combined snapshot including storm scales, and this tool when Kp time series or forecast detail is needed. This gives explicit when-to-use and when-not-to-use guidance, leaving nothing to inference.

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