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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the description's added value is what it discloses beyond them: a hard result cap of 25, that only 'active gauges with current data' come back, and that city searches include distance. It does not mention any rate limits or auth expectations, which keeps it short of a 5 for a tool with no annotation gaps to excuse.

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, all front-loaded: purpose first, result shape second, exclusions and sibling routing last. Every clause carries information an agent needs to select and call the tool; nothing is repeated from 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?

The tool is simple (4 flat, all-optional parameters, output schema present), and the description covers selection criteria, the two input modes, the coordinate exclusion, and the result cap. Return-value detail is rightly left to the output schema.

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, but the description adds meaning the schema does not: the two mutually exclusive search shapes (state+name vs. place) and the explicit rejection of coordinates, which steers the agent away from an invalid input it might otherwise invent. It adds little about radius_miles beyond the schema, so it is not a 5.

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 names a specific verb and resource ('find USGS river or stream gauges (site numbers)') and states the two supported search modes: by state plus river name, or near a US city/town. It explicitly distinguishes itself from the sibling tool by saying it 'does not return readings' and pointing to get_river_conditions.

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?

It states the triggering condition ('when the user wants to find ... gauges'), gives a negative constraint ('does not accept coordinates'), and names the alternative tool with the condition that selects it ('use get_river_conditions for flow and gage height'). This is explicit when-to-use, when-not-to-use, and alternative routing.

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