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

Annotations already declare readOnlyHint, openWorldHint, and idempotentHint, which cover the core behavioral traits (no side effects, repeatable). The description adds detail about the output content (fields included), but it does not disclose limitations such as maximum number of comps, ordering, or behavior when no comps exist. It neither contradicts nor substantially extends the annotation-provided safety profile.

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 description is a single, compact sentence that front-loads the core purpose and then enumerates the returned fields. It contains no filler or redundancy. It could be slightly more structured (e.g., separating purpose from output details), but it is efficiently written and easy to parse.

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 does provide a useful field list, which is necessary for an agent to understand the shape of results. However, it omits structural context such as whether the response is an array, whether results are ordered, and whether 'expand' alters the fields listed. For a simple read-only tool with full schema coverage, it is adequate but not complete.

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 both 'zpid' and 'expand' already described in the input schema. The description does not add any additional parameter meaning beyond what the schema provides. Baseline of 3 is appropriate because the schema fully carries the parameter documentation burden.

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 clearly identifies the resource ('comparable homes Zillow uses to value this one') and implies the verb 'return'. It is specific enough to distinguish from generic 'nearby homes' tools, though it does not name siblings explicitly. The phrase 'uses to value this one' grounds it in Zillow's valuation process, which is a unique angle.

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?

No guidance is provided about when to use this tool versus alternatives. There is no mention of use cases, prerequisites, or when to choose zillow_nearby_homes or zillow_zestimate instead. An agent must infer usage from the name and description alone.

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