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

No annotations are present, so the description carries the full burden. It clearly implies a read-only 'Fetch' operation and discloses the full set of return data, including licensing and readership signals. However, it does not mention error handling, not-found behavior, or rate limits, which prevents a perfect score.

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 description is a single dense paragraph with every clause adding value: it specifies the resource, input format, return fields, and usage guidance. No filler or redundant text is present.

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 simple getter with one parameter and no output schema, the description covers the input requirements, return value contents, and fallback to search_castles. It omits error cases or what happens if no match is found, but these are minor gaps for a fetch-by-identifier 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?

The schema only says 'Slug (preferred, e.g. "himeji-castle") or exact name', but the description enriches this by showing the exact example 'palace-of-versailles', emphasizing the preferred format, and adding the fallback advice. This goes well beyond the schema's generic parameter description.

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 description uses a specific verb ('Fetch') and resource ('one landmark's full record'), and lists the specific fields returned (coordinates, founding year, fame rank, photo, Wikipedia link, readership signals). It also distinguishes itself from search_castles by specifying that it takes a slug or exact name, making the tool's scope clear.

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?

The description explicitly says 'Unsure of the slug? Call search_castles first', providing a clear alternative path. It also states the preferred input format (slug) vs exact name, giving direct guidance on when to use this tool versus searching.

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