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

Annotations already declare read-only, idempotent, closed-world behavior, so the safety profile is covered. The description adds context annotations cannot: the data vintage (FY 2027), the bedroom range covered, that output includes one- and five-year 2-bedroom change, and that results are sorted by the chosen bedroom count.

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?

A single dense sentence carries the operation, scope, and output shape, followed by one short usage sentence. No filler, and the most decision-relevant detail (counties compared, bedroom sorting) is front-loaded.

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 conveying what comes back: FMRs by bedroom count plus one- and five-year 2-bedroom changes, sorted. That is close to complete for a two-parameter read tool, though it could say more about error behavior for unknown counties.

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%, with minItems/maxItems and the bedroom sort semantics already documented in the schema. The description restates the 2–10 county bound and the studio-to-4-bedroom range but adds no format examples or edge-case behavior beyond that baseline.

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 (compare) and resource (HUD FY 2027 Fair Market Rents), plus the exact scope: 2 to 10 counties, studio to 4-bedroom. This scope naturally separates it from siblings like get_fmr_by_county, get_fmr_by_zip, and get_state_fmr_summary, which are single-place or aggregate lookups.

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 closing sentence gives concrete usage contexts — comparing rental markets or voucher rent ceilings — which tells an agent when this multi-county comparison is the right pick. It stops short of explicitly naming the sibling tools and when not to use this one, so it is clear context without full routing guidance.

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