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

Annotations already cover readOnly, idempotent, openWorld and non-destructive, so the bar is lower. The description still adds real context beyond them: "Free, no key" tells the agent no authentication is required, and the parenthetical previews the payload contents. It does not mention network latency, failure behavior when no stations exist, or distance units.

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?

Two compact fragments, front-loaded with the core capability and no filler. The telegraphed style ("Free, no key.") trades a little readability for density but wastes no words.

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?

An output schema exists, so return values need not be explained, and the annotations carry the safety profile. What remains missing for a spatial lookup tool is coordinate format/units, the meaning of `n`, and behavior on empty results — enough gaps to keep it at minimum viable.

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 0% and the description never mentions any of the three parameters. It does not state that lat/lon are decimal degrees or WGS84, nor what the `n` result limit controls or that it defaults to 5, so the description fails to compensate for the undocumented schema.

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?

"Nearest weather stations to a point" names a specific resource and spatial scope, and the parenthetical enumerates the returned fields (name, WMO id, distance, years of record). It is clearly distinct from the generation/analysis siblings (generate_epw, analyze_epw), though it never explicitly says so.

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?

There is no statement of when to call this versus the sibling tools, nor any prerequisite or follow-up guidance (e.g., use this to find a station before calling generate_epw). Usage is only inferable from the purpose sentence itself.

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