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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint false. The description adds valuable behavioral context beyond these: it discloses 'No API key required', the source as 'official German Weather Service real-time observations', the 'nearest DWD station' selection behavior, and the full list of returned measurements. It does not mention rate limits or data freshness, but for a read-only open-data tool the added context is meaningful.

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 compact and front-loaded: the first sentence states what the tool does, the second lists return fields, and the third covers source, coverage, authentication, and licensing. Every sentence earns its place, and the most critical scoping constraint ('Coverage: Germany only') is emphasized clearly. No filler or tautology.

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?

Given the low parameter complexity (2 required coordinates + 1 optional units), a 100%-covered input schema, rich annotations, and an available output schema, this description is fully sufficient for an agent to select and invoke the tool. It supplies the essential non-schema context: geographic scope, data source, nearest-station semantics, authentication requirements, and the returned weather variables. Nothing critical for correct invocation 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%, so the baseline is 3 even without additional description detail. The description reinforces the coordinate-based usage ('any location in Germany' maps to latitude/longitude) and mentions units in return fields (°C, hPa), but it does not explain the units parameter's dwd/si distinction beyond what the schema already provides. It adds little value over the well-documented schema.

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 and resource: 'Get current weather conditions for any location in Germany from the nearest DWD station.' It also enumerates the exact return fields (temperature, humidity, wind, precipitation, etc.), making the tool's scope unambiguous. Its explicit 'Coverage: Germany only' and DWD source distinguish it from generic weather-current siblings like weather.conditions.current and weather.weatherapi.current.

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?

Clear context is provided: this tool is for current weather in Germany from official DWD observations, and 'Coverage: Germany only' tells the agent when it applies. However, it does not explicitly name alternatives or state when not to use it (e.g., for forecasts or non-German locations). It also does not mention the sibling brightsky.weather.observations, which could be confused with this tool.

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