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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds substantial extra context: US-only coverage, max five sites and 366 days, date window from 1900 to today UTC, and output file expiry of about an hour. These are operational constraints an agent cannot derive from annotations or schema.

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?

Front-loaded with the use case, then constraints, then exclusions in three dense sentences with no filler. Each clause (US-only, 5 sites, 366 days, file expiry, exclusions) carries actionable information.

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?

With an output schema present and annotations covering safety semantics, the description supplies everything else an agent needs: scope limits, geographic restriction, date bounds, artifact lifetime, and disqualifying use cases. No gaps remain for correct invocation.

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; the description still adds the 366-day span limit, the five-site cap, and the framing of thresholds as rain/heat/snow/freeze/wind day rules for construction delays. That goes slightly beyond what the per-parameter schema text already states.

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?

States a concrete verb and resource: reads station observations and generates Excel/CSV weather logs with rain-day counts. The opening 'when the user wants weather history' plus the explicit exclusion of forecasts/current conditions/certified reports makes the function unambiguous relative to a sibling like find_weather_stations.

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?

Provides both triggers ('weather history, historical weather data, historical weather by date and location, or a daily weather data download') and explicit when-nots ('Do not use for forecasts, current conditions or certified weather reports'). Nothing is left to inference about routing.

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