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

Annotations already carry readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered. The description adds that the output consists of assessed value and tax paid per year, which is mildly informative, but it does not describe response structure, pagination, or any edge-case behavior. It adds some value without contradicting the 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?

A single sentence that leads with the core data returned (assessed value and tax paid) and ends with a scope qualifier. Every word earns its place; there is no fluff or redundancy.

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 simple read-only lookup with two fully documented parameters and no output schema, the description adequately tells the agent what it will receive. The only missing piece is an explicit statement of the required input (zpid), but that is already enforced and documented in the schema, so the description does not need to repeat it.

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%, with zpid and expand fully documented in the schema. The description does not add parameter-level detail beyond what the schema provides, so the baseline score of 3 applies. No param information is missing.

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 names the resource ('Assessed value and tax paid by year for a home') and the scope ('as far back as Zillow records them'), which distinguishes it from sibling tools like zillow_price_history (sales prices) and zillow_zestimate (estimated value). It lacks an explicit verb like 'retrieve' or 'get', but the meaning is 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?

No guidance is given about when to choose this tool over alternatives such as zillow_price_history or zillow_property_facts. The phrase 'as far back as Zillow records them' hints at historical data but does not state usage conditions or exclusions. An agent must infer when this is the right tool.

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