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

With no annotations at all, the description carries the full burden, and it does disclose several real traits: the call is free, results are real-time/latest, the search radius is capped at 25 km, and at most 3 gauges are returned. It omits what happens with an invalid or non-Canadian postal code, whether an empty result is possible in sparse areas, and the units/format of returned levels.

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 terse sentences with no filler; the 'FREE' marker and the 25 km / nearest-3 limits are front-loaded. Nothing is wasted, though the telegraphic style leaves the radius and count constraints slightly ambiguous in phrasing.

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 one-parameter read tool with no output schema and no annotations, the description conveys the essentials of scope and result size but leaves the return shape undocumented — an agent cannot know field names, units, or whether flows and levels are returned together. Adequate, not complete.

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 0%, so the description must compensate, and it does add one meaningful fact: the postal code must be Canadian. It says nothing about format expectations (spacing, case, six-character alphanumeric), and the single parameter's required status is only visible from the 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?

Names a specific resource (river/lake water levels and flows at gauges) and a specific scoping rule (within 25 km of a Canadian postal code, nearest 3). Clear enough that an agent can distinguish it from a trend or flood-alert tool by subject matter, though it never explicitly contrasts itself with flood_watch or gauge_trend.

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?

There is no when-to-use or when-not-to-use guidance and no mention of the siblings flood_watch and gauge_trend, which an agent would plausibly confuse with a level-lookup tool. The only usage-adjacent signal is the constraint 'nearest 3' inside a 25 km radius, which limits results rather than guiding selection.

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