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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds genuinely new behavior: nearest-first ordering, caps (15 towns / 20 places), deduplication by nearest point, exclusion of a town's own sights, straight-line rather than road distances, and the failure mode ('an unknown place or nothing within the radius returns an error message'). This is exactly the context annotations cannot convey.

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?

Front-loaded with purpose and mode selection, then constraints, then alternatives. Information density is high, though it runs long and repeats the schema's place-vs-lat/lng rule verbatim, which is the only real redundancy.

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 restated, yet the description still gives enough about the two view shapes, limits, distance type and error behavior that an agent can call this correctly without opening the schema. Nothing material is missing for a read-only lookup 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 coverage is 100%, so the baseline is 3, and the description earns above that by explaining the effect of omitting type (group-by-town day-trip view vs. flat list), how to combine place or lat+lng, and the distance semantics that govern radius_km. It does not add format or ordering detail for lat/lng beyond 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?

Specific verb ('List') plus resource ('the places Meridian Dispatch covers') with explicit scope ('near a place or a coordinate, nearest first') and two operating modes (day-trip view vs. typed flat list). It also distinguishes itself from siblings by name, telling the agent what get_destination and search_guides cover instead.

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?

States when to use each mode ('Without type it answers a day-trip question... With type it returns a flat list'), how to supply the origin, and routes to alternatives explicitly: 'For the sights inside one town use get_destination; to search by theme use search_guides.' Nothing is left to inference.

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