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

With no annotations, the description must carry behavioral disclosure, and it does: it states the data source (Open-Meteo archived model runs), approximate resolution (2 km), coverage period (2018 onward), and the returned variables (daily temperature and precipitation). It doesn't mention billing requirements or potential data gaps, but the core behavior is transparent.

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?

Two short sentences with no filler. The first states the operation and the second adds return values, source, resolution, and coverage—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 data-retrieval tool with an output schema, the description is sufficiently complete: it identifies required inputs, the data source, spatial resolution, temporal coverage, and return variables. It could additionally say 'not for forecasts/current conditions', but the siblings and the word 'historical' largely cover that.

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 83%, above the 80% threshold, so the schema already documents latitude, longitude, start_date, end_date, and npub. The description only adds 'location and date range' and doesn't need to repeat parameter details; dpop_token remains undocumented but that is a schema gap, not primarily the description's responsibility.

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?

Description uses a specific verb 'Get' with a resource ('historical weather data') and specifies the location/date range, returning daily temperature and precipitation. It also distinctively names Open-Meteo archived model runs and coverage from 2018 onward, which separates it from weather_current and weather_forecast.

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 word 'historical' and 'archived model runs' imply use for past dates rather than current/future conditions, but the description never explicitly says 'use this for past data, not weather_forecast or weather_current'. The guidance is clear enough to infer, but no alternative is named.

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