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

Annotations already mark the tool as readOnly and idempotent, and the description adds meaningful behavioral detail beyond that: it blends months weighted by days from ~30 years of ERA5 history, reports the same window across the last 5 individual seasons, and returns 'insufficient' rather than unreliable odds for short histories. This gives the agent a clear model of how the result is produced.

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 front-loaded with the core purpose and then provides dense, useful context about methodology, outputs, alternatives, and edge cases. It is slightly long and some output details overlap with what an output schema likely already conveys, but every clause contributes selection or invocation value.

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 three parameters, full schema coverage, annotations, and an output schema, the description is complete: it covers what the tool does, how the data is computed, when to use it instead of siblings, parameter constraints, and failure behavior. 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 coverage is 100%, so the baseline is 3, and the description adds extra value by stating the 31-day window max and reinforcing the date format. It also clarifies the conceptual meaning of a 'trip window' in a way the schema alone does not, which helps an agent construct valid requests.

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 opens with a precise statement: 'Historical odds for a SPECIFIC trip window at one resort' and gives concrete examples like 'Whistler on March 27' and 'Vail Jan 10–17'. It clearly distinguishes this tool from the weather forecast and monthly-snow siblings, so an agent can tell exactly what resource it operates on.

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 explicit routing guidance: 'This is HISTORY, not a forecast and not a prediction — for the next 14 days use get_weather_forecast, and for a whole-month question use get_monthly_snow.' It also states the behavior for insufficient data, saying windows with under 5 tracked seasons return 'insufficient rather than thin odds.'

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