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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds real context beyond that: data provenance (FHFA back to 1975), what the sub-ZIP nbhd* fields mean, and a caveat that they represent POSITION rather than a neighborhood forecast. The forward reference to '_units' is unexplained and undefined in the schema.

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?

Information-dense and front-loaded: the primary output set comes first, then the sub-ZIP caveat. It is slightly cluttered by the dangling '_units' pointer, but no sentence is purely redundant.

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?

With no output schema, the description carries the return-value burden and does so by naming the forecast, rent, neighborhood signals, and sub-ZIP fields. Annotations cover the safety profile, and the only omissions are rate limits/auth and explaining the '_units' reference.

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 description coverage is 100%, so the baseline is 3. The description restates the property_type values (sfr | condo | townhome | multi), which is marginally helpful since the schema lists no formal enum, but this duplicates the schema's own field text rather than adding meaning.

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 verb ('look up') and resource ('a US address or bare 5-digit ZIP') and enumerates the returned dimensions: appreciation forecast, market rent, and neighborhood signals. This is clearly distinguishable from analytical siblings like buy_vs_rent or affordability, though it never names an alternative to contrast against.

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?

It implies when to pass a full address versus a bare ZIP (the nbhd* sub-ZIP fields only appear with a street address), which is useful. But it gives no guidance on when to choose this tool over affordability, affordable_price, compare_areas, or buy_vs_rent, so the agent must infer routing.

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