county_at

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds real behavioral context beyond that: the returned chain of counties, the meaning of 'attached to' and 'contested', the 2000 cutoff, and the caveat that some results need manual verification.

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 purpose is front-loaded in sentence one, and each following sentence carries genuine domain information rather than filler. It is longer than strictly necessary and slightly discursive, but no sentence is wasted.

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 usefully characterizes the return (holder(s), full chain, within-a-year changes) and the tool's scope limits. It omits edge-case behavior such as out-of-range dates or points outside the covered area, which keeps it from a 5.

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 latitude, longitude, date and refresh are already fully documented, including the year/month expansion behavior. The description adds no syntax or format detail beyond the schema, so the baseline 3 applies.

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 opening sentence states a precise verb and resource: which county held a point on a date, plus the act that made it so. That is a specific point-in-time lookup that is inherently distinguishable from siblings like county_history (history of a named county) without needing to name them.

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 strong contextual guidance: records were made by the county that held the place THEN, boundary_change_within_a_year should be checked by hand, and the atlas ends in 2000 and holds no towns or townships. It never explicitly names an alternative sibling or states when not to use this tool, so it stops short of a 5.

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