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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description earns credit beyond that by naming the return aggregates and warning that many gauges publish daily means for discharge only, a real data-availability caveat the agent could not infer elsewhere.

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 short sentences, no waste: output content first, usage contexts second, data caveat last. Everything is front-loaded and scannable.

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?

No output schema exists, so spelling out the returned aggregates is necessary and done. Minor gaps remain -- how 'change' is computed or reported, unit/timezone handling, and behavior on missing data -- but nothing that would prevent a correct call.

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 site, days and the parameter enum are fully documented in the schema. The description adds only terminology mapping (streamflow = discharge, stage = gage_height) and the default of daily means, which is marginal value over the structured fields.

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?

Specific verb+resource: daily mean streamflow or stage for a USGS gauge over 2-366 days, and it enumerates the returned aggregates (first, last, low, high, mean, change). What it lacks is explicit differentiation from the sibling get_river_level, which the agent must infer from the word 'history'.

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?

Gives concrete use contexts -- trend, drought, and 'is the river rising' questions -- which clearly frames when to reach for this tool over a point-in-time reading. There are no explicit exclusions or a named alternative for current conditions, so it stops short of a 5.

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