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

Annotations already declare readOnlyHint, openWorldHint, and idempotentHint, covering safety and idempotency. The description adds behavioral detail: events are listed newest first and include price, change, and source. This goes beyond the annotations and gives the agent a sense of the response shape without contradicting any 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 description is a single, tightly packed sentence that leads with the core purpose and immediately lists the event types, ordering, and key fields. There is zero fluff or redundant phrasing, making it easy to scan and understand quickly.

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?

Given the annotations cover safety and idempotency, and the schema fully documents both parameters, the description supplies the missing behavioral context: what events are included, the order, and the data fields returned. It does not describe pagination or limits, but for a read-only list tool this is sufficient. No output schema exists, but the description's field list provides the necessary guidance.

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 having detailed descriptions. The tool description adds no additional parameter meaning beyond what the schema provides, so the baseline of 3 applies. It does not compensate for any gaps because there are none.

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 states exactly what the tool returns: every listing, price cut, pending, sale, and delisting event for a home, ordered newest first, including price, change, and source. This clearly distinguishes it from siblings like zillow_tax_history or zillow_comps, which cover different data types. The verb is implicit but the resource and scope are unambiguous.

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?

The description does not explicitly state when to use this tool versus alternatives. It implies use for price history data, but there is no guidance like 'use this for historical price events' or 'not for tax history.' The context is clear enough for a user who knows the domain, but no explicit exclusions or alternative routing are provided.

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