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

Annotations already declare read-only, idempotent, non-destructive and closed-world, so the safety profile is covered; the description still adds genuinely new behavior: the ~10-minute cache refresh and the explicit failure semantics ('says plainly when live counts are unavailable instead of reporting zero'). That staleness and error-handling context is exactly the kind of detail annotations cannot express.

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 sentences, front-loaded with the core action and scope, then the conditional parameter behavior, then the cache/fallback note. Every sentence carries information an agent needs; nothing is padding.

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 an output schema present, return values need no explanation, and the description still covers the two things an agent cannot infer: the freshness window of the count and the explicit 'unavailable rather than zero' semantics. Nothing needed to call it correctly is missing.

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% (both params fully described with ranges and slug/name formats), so the baseline is 3. The description adds interpretation the schema does not: the budget is an inclusive threshold ('at or under it') applied to the live count, and city must be 'supported'. Modest but real added value.

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 precise verb and resource ('count the live rental listings ... in a supported city') plus the conditional budget behavior, which no sibling (get_plans, list_cities, start_home_search) covers. An agent can distinguish this counting tool from the search and listing tools without opening any schema.

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?

Usage is implied by the conditional budget clause ('if a monthly budget in EUR is given'), and 'supported city' hints at a prerequisite, but there is no explicit when-to-use statement and no routing to alternatives such as start_home_search when the user wants individual listings rather than a count.

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