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

Annotations already cover readOnly, idempotent, non-destructive behavior. The description adds useful context: real-time freshness, NWIS data source, and units for common parameters. It doesn't disclose return format, pagination, or rate limits, so it adds moderate but not extensive behavioral detail.

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 with no filler: the first states the core purpose, the second covers filters with an example, and the third gives use cases. It is front-loaded and every sentence earns its place.

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 simple read-only query tool with well-documented parameters and rich safety annotations, the description is sufficiently complete: it gives source, filters, examples, and use cases. It doesn't spell out the response shape or data limitations, but the absence of an output schema is not critical for selecting and invoking this tool.

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 all three parameters. The description adds lightweight examples and units (streamflow cfs, gage height ft), but doesn't substantially improve on the schema's parameter descriptions.

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 clearly identifies the resource (USGS NWIS streamgages) and the operation (retrieving real-time water data), with explicit filter dimensions. It doesn't explicitly differentiate from sibling tools like water_levels or tide_predictions, so it doesn't earn a 5.

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 gives clear context by naming concrete use cases ('flood-stage monitoring, drought tracking, and hydrological research') and notes the filter options. However, it doesn't state when not to use it or point to alternative tools.

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