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

Beyond the readOnly/openWorld annotations, the description discloses genuinely non-obvious behavior: pagination (~41 per page) driven by max_results, the rental building variant that lacks `zpid` and instead carries `lotId`, `buildingName`, a price-to-maxPrice rent range, `units` and `availableUnits`, and the billing model (one unit per result page fetched). These are exactly the traits an agent could not infer from the schema or annotations.

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 most important information (location search, returned fields) is front-loaded, and the rental-building edge case and billing warning are placed after the core usage. It is dense but well ordered; the trailing 'Returns JSON.' sentence is redundant with the opening 'returns the listings as JSON' and is the one piece of dead weight.

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 an 11-parameter scraper with no output schema, the description carries the needed load: it enumerates return fields, explains the anomalous rental-building shape, documents the pagination/cost tradeoff for max_results, and notes proxy_country's role implicitly through the request context. An agent has enough to call this correctly without further discovery.

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%, so the baseline is 3, but the description adds real meaning on top: min_price/max_price also mean monthly rent when status=for_rent, and max_results is framed as collection across multiple pages rather than a single request. The remaining filters (sort, home_type, status) are restated from the schema rather than extended.

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 opens with a specific verb+resource pair ('Searches Zillow for `location` ... returns the listings as JSON') and enumerates the returned fields, so an agent can distinguish it from the other marketplace scrapers in the sibling list (amazon_search, ebay_search, walmart_search) at a glance.

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?

It gives clear operating context: filter with status/min_price/max_price/beds/baths/home_type, sort with sort, and cap collection with max_results. It also advises keeping max_results modest because of per-page billing. What's missing is any explicit statement of when NOT to use it or a pointer to an alternative sibling, so it stops short of a 5.

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