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

Beyond the annotations (readOnlyHint, openWorldHint), the description discloses update frequency (monthly), result limits (up to 10 regions, largest first), pricing ($0.002 USDC per successful call via x402 on Base, Solana, or Arc), and that failed calls are not charged. It also clarifies data provenance (Zillow Research official public data, smoothed, all home types).

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 core purpose is front-loaded in the first clause, followed by compact details on output, limitations, update cadence, and pricing. It is dense but every sentence carries information; no filler or repetition.

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 presence of an output schema and rich annotations, the description covers the remaining gaps an agent needs: data source, index-vs-listings distinction, update frequency, result cap, and pay-per-call mechanics. Nothing critical for correct invocation is missing.

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?

The schema already documents all four parameters at 100% coverage, so baseline is 3. The description adds meaningful context beyond the schema: it explains that region matching returns up to 10 results, largest first, and that output includes state, metro, and county fields.

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 a specific data product (Zillow Observed Rent Index for US metros/cities) and precisely what is returned (latest rent, 12-month change, monthly history). It distinguishes itself from listing-based tools by saying 'Index data, not individual listings,' but does not explicitly name sibling alternatives such as realestate_zillow or rentals scrapers.

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?

Usage is implied by the note that this is index data rather than individual listings, and that listing pages block automated access. However, it does not explicitly state when to choose this tool over alternatives like realestate_zillow or realestate_hotpads_rentals, nor does it provide exclusion conditions or routing guidance.

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