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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint, and destructiveHint false. The description adds valuable behavioral context beyond annotations: the underlying API source (api.weather.gc.ca), data provenance (HYDAT/WSC), no-auth requirement, typical 5-minute reporting interval, and sorted output. These details help the agent set expectations about data freshness and response ordering.

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?

Three sentences carry all essential information: what the tool returns, the lookup key, sort order, update frequency, data source, and auth requirement. No filler or redundant restatement of the schema or title.

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, return-value documentation is unnecessary. The description covers the input key, units, data source, geographic scope, frequency, ordering, and auth. For a two-parameter read-only tool, nothing an agent needs to invoke it correctly 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 schema already documents both parameters well, including an example station number. The description adds the sort-order behavior and ties the 5-minute reporting cadence to the station_number, but it does not substantially extend parameter-level meaning. Baseline 3 is appropriate.

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 ('Get'), a precise resource (real-time water level in meters and discharge in m3/s for Canadian rivers/lakes), and the key lookup key (hydrometric station_number). It also notes the sort order (most-recent-first), which clarifies exactly what the tool returns. The Canadian scope and units distinguish it clearly from sibling tools like msc-geomet.climate.daily or ea-hydrology.readings.

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 implicitly scopes usage to Canadian real-time hydrometric data, which is clear context. It does not name alternatives or state when not to use this tool, but the data source, geography, and real-time nature are enough to route an agent correctly.

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