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

With no annotations, the description carries the full burden and does well: it discloses the accent/case-insensitive matching, the sort order (best-match then fame), the returned fields, and empty-result behavior. It omits any statement about rate limits, permissions, or pagination behavior beyond the limit parameter.

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?

Three tight sentences, front-loaded with the verb and scope, then filters, then results and fallback. No filler sentences; every clause earns its place.

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?

For a 4-parameter read tool with no output schema, the description compensates by enumerating the returned fields (coordinates, founding century, fame rank, atlas/Wikipedia links) and the result ordering. It is nearly complete, missing only error/rate-limit guidance.

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 all four parameters are already documented in the schema; the baseline is 3. The description adds marginal value by restating the country-name-or-ISO and category filtering behavior and implying query is a partial name, but adds no format details 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?

States a specific verb (search), resource (9,079 castles/fortresses/palaces/ruins), and matching semantics (accent- and case-insensitive substring). This clearly separates it from siblings like get_castle (single lookup) and castles_near (proximity).

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?

Gives clear usage context: optional country and category filters, plus a concrete recovery action when nothing matches ('retry with a shorter fragment'). It stops short of explicitly naming sibling alternatives (e.g., use get_castle for full detail, castles_near for geography), so it is clear but not exhaustive.

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