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

Annotations only declare readOnlyHint and openWorldHint, but the description adds substantial behavioral context: monthly refresh cadence, ZIPs with too few rentals are not covered, and the x402 pricing model ($0.002 USDC per successful call, failed calls not charged) with the accepted chains. These are exactly the facts an agent needs before committing a paid call.

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?

Dense but front-loaded: the identity of the data comes first, then scope caveats, then pricing. It is a single long sentence with heavy parenthetical nesting in the opening clause, which costs a bit of readability, but every clause carries 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?

An output schema exists, so the description does not need to enumerate return fields in depth, yet it still summarizes what comes back (latest value, 12-month change, history, city/metro/county). Combined with coverage limits and billing behavior, an agent has everything needed to call and interpret it correctly.

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 both `zip` and `months` are already documented with format and range. The description mentions 'latest monthly value, change vs 12 months earlier, monthly history', but that describes the response rather than adding meaning to the input parameters, so baseline 3 applies.

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?

Names a specific verb and resource: 'Typical market rent for a US ZIP code from the Zillow Observed Rent Index (ZORI)'. It also explicitly distinguishes itself from listing-based siblings by stating it is index data, not individual rental listings.

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 makes clear this is the ZORI index route and notes that zillow.com listing pages block automated access, which implicitly steers an agent away from a live-scrape approach toward sibling listing tools like realestate_zillow_rentals. It stops short of naming an alternative tool or stating an explicit when-not-to-use condition.

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