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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds genuinely useful behavior beyond that: it costs 1 credit and returns full listing records. It omits pagination behavior and any caching semantics despite a cache_max_age parameter.

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 short sentences, front-loaded with the purpose, then cost and input rule. The middle sentence partly restates the first ('search results for a location'), so there is minor redundancy, but nothing is bloated.

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 a 5-parameter tool with no output schema and 40% coverage, the description covers cost, input mode, and rough return shape, which is adequate. It leaves listing_type semantics, page numbering, and cache_max_age entirely unaddressed, which an agent would need to guess.

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?

With only 40% schema coverage, the description carries real weight, and it does add the non-obvious one-of constraint (location OR url) that the schema does not encode since nothing is required. But listing_type (sale/rent), page, and cache_max_age are undocumented in both places, leaving over half the parameters unexplained.

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 ('Search Zillow listings by location') and clarifies it returns full listing records rather than a single property. It does not distinguish itself from zillow_property or the redfin siblings, so an agent must infer that this is the listing-level search while those are detail/vertical tools.

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?

'Pass either `location` or `url`' gives concrete input-selection guidance for the two entry modes. However, there is no guidance on when to prefer this over zillow_property or redfin_search, and no exclusions or prerequisites are stated.

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