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

Goes beyond the annotations with concrete operational facts: no login, no browser required, 1 credit per result, and failed items are free. That cost and failure semantics are exactly the kind of behavior an agent cannot get from readOnlyHint/openWorldHint. It still says nothing about pagination behavior or rate limits, hence not a 5.

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 action and scope, then the return fields, then the cost model. No filler and no repetition of the schema.

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 only two parameters, no output schema, and annotations covering safety, the description supplies the missing return-value summary and the credit-cost model that nothing else conveys. Minor gap: no mention of result ordering or what a 'failed item' looks like.

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%, with the location parameter already documenting city+state, URL slug, and full URL formats plus the 820-listing pagination ceiling. The description adds only the loose phrase 'by city/location', 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 ('Search Zillow for-sale listings by city/location') and enumerates the fields returned (price, beds, baths, square footage, Zestimate, type, status). It implicitly scopes to for-sale rather than rentals, which is a meaningful distinction, but it never contrasts itself with any sibling tool by name.

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?

Implies usage context ('by city/location') and implicitly excludes rentals by saying 'for-sale', but gives no explicit when-to-use vs when-not guidance and names no alternative tool. Adequate but leaves the agent to infer routing.

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