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

Annotations already declare readOnly, idempotent, open-world, non-destructive, so the safety profile is set. The description adds real context beyond that: results include site numbers, current reporting status, latest stage and flow, and are ordered with active gauges first — useful for interpreting a response with no output schema. It does not mention result caps or pagination.

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?

A single dense sentence that front-loads the search modes and ends with what is returned. It earns most of its words, though the parenthetical examples duplicate the schema examples and the sentence is long enough to be slightly hard to scan.

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 no output schema, the description correctly spends words on the return shape (site numbers, reporting flag, stage, flow, ordering). Remaining gaps are minor for a discovery tool: no note on parameter combination behavior, result limits, or empty-result handling.

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 all five parameters are already documented with examples and constraints. The description echoes the same examples ('mississippi st louis') and mentions the modes but adds no new semantics such as what happens when query and state are both supplied. 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?

States a specific verb and resource (search USGS stream gauges) and enumerates the three search modes (river/place name, state, radius around a lat/long). This clearly distinguishes it from the get_river_level / get_river_history / get_flood_forecast siblings, which look up a known site rather than discover one.

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 implies usage by giving example queries and describing each search mode, so an agent can infer which input to supply. However, it never says when to prefer this tool over a sibling (e.g., 'use this first to find a site number, then call get_river_level'), nor whether criteria can be combined or which takes precedence.

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