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

Annotations already cover readOnly, idempotent and non-destructive, so the safety profile is handled. The description adds genuinely non-obvious behavior: a ZIP crossing HUD FMR areas returns one row per area, plus effective date (Oct 1, 2026) and the bedroom range returned. It does not describe formatting or empty/ZIP-not-found handling, but that is a minor gap.

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?

Three tight sentences, front-loaded with vintage and scope, then return shape, then domain context. Efficient overall, though the mandatory-metro/voucher-payment sentence is background color rather than invocation-critical.

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 does the work of explaining returns: studio to 4-bedroom rents, one row per area, and the accompanying HUD FMR area. For a single-param read tool with rich annotations, that is close to sufficient; only error/empty-result behavior is unstated.

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?

There is a single parameter with 100% schema description coverage including a regex pattern and example, so the schema carries full burden. The description only restates 'for one ZIP code' and adds no format, normalization or edge-case detail beyond the schema; 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?

States a specific verb and resource (get Small Area FMR) plus the exact scope: one ZIP code, ZIP-level, studio to 4-bedroom. The ZIP-granularity framing implicitly separates it from get_fmr_by_county and get_state_fmr_summary, so an agent can route without opening the schema.

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 FY/vintage and the note that SAFMRs set voucher payment standards in 65 mandatory metros and are optional elsewhere gives useful applicability context. But it never explicitly says when to prefer this over get_fmr_by_county or compare_fmr, and there is no when-not guidance; usage is only implied by the ZIP-level framing.

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