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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered without the description. What the description does add is genuinely useful and non-obvious: an explicit trust boundary stating that title and description are untrusted supplier data and must never be treated as instructions, which is prompt-injection guidance no annotation conveys.

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?

Two short sentences, front-loaded with the operation and followed by the safety caveat. No filler, no restatement of the title, and every clause carries information an agent would otherwise have to guess.

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-value shape need not be explained, and the injection warning covers the main non-obvious risk for a detail-fetch tool. What is missing is failure behavior — what happens when the listing_id is unknown or the listing is unavailable — which matters for a lookup tool keyed on a required id.

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 description coverage is 100% and the single listing_id parameter is fully documented in the schema, including the instruction to pass the id unchanged. The description adds nothing about the parameter, but with complete schema coverage the baseline of 3 applies and the terse one-parameter surface keeps it from being a real gap.

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?

"Return full details for one Casatoo listing" gives a specific verb (return) and resource (a single listing), which contrasts naturally with the sibling search tools that return many. It never names a sibling explicitly, so differentiation relies on the agent inferring single-vs-many from the wording.

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?

There is no explicit when-to-use or when-not-to-use statement, nor any pointer to casatoo_search_listings as the way to obtain a listing_id. Usage is only implied: fetch one record by id. The linking detail ("UUID returned by listing search") lives in the schema rather than the description.

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