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

Annotations already declare read-only, idempotent, non-destructive, closed-world behavior, so safety is covered. The description adds genuinely useful context beyond that: the miss case 'returns found false and does not substitute another home,' which tells the agent not to expect a sibling listing fallback. It stops short of describing pagination or response shape details, but for a single-item read this is solid.

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 front-loaded sentences with no filler: the returned-field inventory comes first, the edge-case behavior second. Every clause earns its place given there is no output schema to carry the field list.

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 no output schema, the description compensates by enumerating return fields and documenting the not-found behavior, which is the key completeness risk for this tool. Minor omission: it does not explain how stay_nights changes the 'stay fit' signal, though the schema covers the parameter's allowed values and purpose.

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% and both parameters carry their own descriptions (listing_id sourced from search_rentals, stay_nights scoped to the fit check). The description does not add syntax or format detail beyond the schema, so the baseline 3 applies.

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 and resource ('Returns one RentalHunter listing by id') and then enumerates exactly what comes back (rent in local currency, locality, stay fit, furnishing, deposit, lock-in, verification badges, freshness, link). An agent can distinguish this single-item fetch from the sibling search_rentals list tool without opening either 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 rather than stated: retrieving one listing by id, with the id obtainable from search_rentals (which the schema notes, not the description). There is no explicit 'use this after search_rentals when you need full detail' routing, and no when-not guidance. Adequate but with a clear gap.

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