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 context about the HARMONIE model and the 60-hour forecast horizon, which is useful but minimal. It does not disclose potential model update delays or output specifics, but given the annotations, this is acceptable.

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 description is a single 13-word sentence that front-loads the key information (multi-hour, model, location, horizon). It contains no redundant words or filler, and every phrase 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 straightforward read-only weather forecast tool with a rich input schema and an output schema, the description covers essential purpose and scope. It could mention units or timezone, but those are likely handled by the schema/output schema. The lack of explicit sibling contrast is a minor gap, but the tool is simple enough that the description is nearly complete.

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?

The input schema has 100% coverage with descriptions for place, timestep, and parameters, so the description adds no new parameter-level information. It mentions 'place name in Finland' but the schema already explains the place parameter with examples. Thus, the baseline score of 3 applies as the description neither enhances nor harms parameter understanding.

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 the tool provides a 'Multi-hour HARMONIE forecast' for a place in Finland, specifying the model, geographic scope, and time horizon. This distinctively separates it from observational sibling tools like 'latest_observations' and 'recent_observations' by focusing on future prediction rather than current or past data.

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 gives a clear context for use: it is a forecast for Finland, so an agent would invoke it when future weather data is needed. It does not explicitly mention alternatives or exclusions, but the 'forecast' wording implicitly contrasts with observation tools. This satisfies 'clear context' though it lacks explicit when-not guidance.

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