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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint, covering safety and idempotency. The description adds practical context: 'No auth — USGS public domain, unlimited calls,' which informs agents about rate limits and access requirements. This goes beyond annotations without contradicting them.

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?

The description is three sentences, front-loaded with the primary purpose, then a key field importance note, then sibling differentiation and auth info. Every sentence earns its place with no redundancy. It is concise and well-structured for quick scanning.

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?

Given the tool has an output schema (indicated in context), the description need not explain return values. It covers the primary function, key usage nuance (drainage_area importance), alternative tool relationship, and access constraints. For a single-parameter read-only tool, this is complete and sufficient for an agent to call it correctly.

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%, and the schema's site_no description includes format examples and guidance to use water.sites for discovery. The tool description does not add new parameter-specific semantics beyond reiterating the site_no usage context. Since the schema handles parameter documentation well, a baseline score of 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?

The description clearly states the tool retrieves detailed metadata for a specific USGS hydrologic monitoring station, enumerating key fields (drainage area, HUC, coordinates, altitude, etc.). It explicitly differentiates from the sibling water.sites by describing this as deep metadata for a known site versus a search tool. The verb 'Get' is specific and the resource is unambiguous.

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?

Provides explicit workflow: 'Use water.sites first to find the site_no, then call this for full station context.' It names the alternative (water.sites) and explains when to use each, making the decision clear. No ambiguity about when to choose this tool over siblings.

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