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

Annotations already declare read-only, idempotent, non-destructive and closed-world, and the description goes well beyond them: it discloses coverage limits (population floor, latitude cutoff), the result cap of 5 candidates, the presence of a place_token in each result, and a recovery strategy for empty results. That is exactly the kind of behavioral context an agent cannot get from the structured fields.

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?

Four short sentences, each carrying distinct information: scope, result shape, query narrowing, and fallback. The dataset limits are front-loaded before the usage tips, and nothing is repeated from the schema or annotations.

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 one required string parameter, no output schema, and no nested structures, the description covers everything an agent needs: what it searches, its coverage boundaries, how many results come back, what the results contain, and what to do on a miss. No meaningful gap remains.

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% and the single parameter already documents the comma-separated region/country form, so the baseline is 3. The description adds the reason for that syntax ('to narrow the search'), turning a format note into actionable search strategy, which is a modest but real gain over the 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?

States a specific verb and resource ('Look up a town in the Astrodai atlas') and immediately bounds the dataset: towns above ~15,000 people, nothing at or beyond 66 degrees latitude. No sibling tool does place lookup, so there is no ambiguity to resolve, and the scope constraints make the tool's domain unmistakable.

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?

Explains the workflow role by noting the returned place_token is 'for the other tools', which tells the agent this is a first step feeding later calls, and gives explicit fallback advice ('If nothing matches, try the nearest larger town'). It stops short of naming a specific alternative tool or stating when not to call it, but the sibling set contains no competing search tool.

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