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

Annotations cover the safety profile (readOnly, openWorld, non-destructive), and the description adds genuinely useful behavior: the per-page billing model, the advice to keep max_results modest, and a detailed handling of apartment-building rental results (isBuilding, no zpid, lotId, rent range, units/availableUnits). That is well beyond what the structured fields convey.

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?

Front-loads the core action and return shape before moving to filters, sorting and the rental edge case, with no filler sentences. It is dense and slightly long, but each clause (billing, building results) carries information an agent would otherwise miss.

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 takes on the burden of describing return fields and does so thoroughly, including the anomalous isBuilding result shape. Combined with the billing note, an agent has everything needed to call this correctly and cheaply.

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%, so every parameter is already documented in the schema; the description mostly restates the same filter names without new syntax or format detail. Baseline 3 is appropriate for a fully-covered schema where the description only echoes the fields.

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?

Opens with a specific verb+resource (searches Zillow for a location) and enumerates the exact fields returned, so an agent knows precisely what it gets back. It is the only Zillow-family tool among the siblings, and the listing/scraping scope is unmistakable.

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 in-tool guidance: which parameters filter (status, price range, beds/baths, home_type), which sorts, and how max_results collects across pages. It does not, however, say when to prefer this over neighbouring tools such as booking_hotels or google_search, so the routing guidance stops short of exclusions.

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