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

Annotations only say read-only and open-world; the description adds substantial context beyond them: pricing at $0.002 USDC per successful call via x402 (Base/Solana/Arc), no charge for failed calls, a hard 350-row ceiling, and known coverage holes in download data. These are exactly the operational facts an agent needs before paying for a 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?

Front-loaded with the capability and modes, then cost and caveats. The long enumerations of returned row fields and the 19-column list consume a lot of space that an output schema arguably covers, but the rest of the text is dense and purposeful with no filler.

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 7-parameter paid third-party data tool with an output schema, it covers source, scope, limits, cost, and coverage caveats. The only gap is guidance on when to choose this over the numerous competing listing tools, which would help an agent make the selection decision.

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 baseline would be 3, but the description adds meaning: the search area is a box around the point (clarifying radiusKm as a half-width), the output ceiling of 350 (bounding limit), and sold-window semantics for soldDays. It doesn't restate the type enum or the lat/lon formats, which is fine since the schema does.

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?

States a specific verb and resource: Redfin US home listings inside a box around a point, sourced from Redfin's own CSV download, with two explicit modes (for sale vs sold). This is concrete enough to distinguish it from the many other real-estate siblings (zillow, estately, hotpads) because the source and coverage are named.

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 explains the mode split (sale incl. coming soon/pre-market, or sold in last N days), the 350 cap, and a key caveat that some MLS listings/areas (e.g. Seattle) are absent. It does not name a specific alternative tool or state when a sibling should be preferred, so it stops short of explicit routing.

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