Get Zestimate history for a property

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

Annotations already declare readOnlyHint, openWorldHint, and idempotentHint as true. The description adds value by explaining the response format (time series with optional rent), the edge case of empty points, and the safety of repeated calls. This goes beyond the annotations without contradicting them.

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 concise at about 4-5 sentences. It is front-loaded with the primary purpose and each subsequent sentence adds key details (use alternative, edge case, safety). No extraneous information.

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 no output schema, the description explains the return shape (time series with date, value, rent) and addresses the notable edge case of empty points. It covers the main usage scenarios sufficiently, though minor details like date ordering or pagination could be added but are not essential.

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. The description restates that either zpid or URL can be provided, which reinforces the mutual exclusivity but does not add substantial new meaning beyond the schema descriptions.

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 tool's purpose: retrieving historical Zestimate values for a property. It specifies the input methods (zpid or URL) and explicitly differentiates from the sibling tool zillow_get_property by highlighting that it returns trends rather than a single current value.

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 provides explicit guidance on when to use this tool: 'call this tool when you need the trend' versus the current Zestimate from zillow_get_property. It also addresses the edge case of non-Showcase listings where an empty points array is expected and a note is returned, distinguishing it from a genuine lack of history.

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