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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description's value-add is real: it discloses provenance (40th-percentile voucher rent in the site's Section 8 extract) and explicit failure behavior (missing ZIP or multiple town rents returns a message rather than guessing a number). It does not describe the return shape or how the FY vintage affects results.

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 what is returned and what it is not, followed by the edge-case behavior. No filler; every clause carries information an agent can act on.

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 two-param read tool with a closed-world annotation set, the description covers purpose, provenance, and failure mode well. Since there is no output schema, it could more explicitly state the return value's form (e.g. monthly dollar figure per bedroom count), leaving a small gap.

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%; both zip and bedrooms are documented in the schema (5-digit ZIP, 0 = studio, 4 max). The description's 'studio through 4' restates what the schema already declares, adding no new syntax or format detail, so the 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 precise verb+resource (lookup HUD Fair Market Rent for a ZIP and bedroom count) and names the scope of the value (FMR/Small Area FMR, studio through 4). It explicitly distinguishes itself from the market-rent sibling by saying 'not a market-rent estimate', so an agent can route between this and estimate_rent without opening either 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 description establishes the correct usage context (voucher/Section 8 rent lookup against the published FY extract) and clarifies it is not a market-rent estimate, which implicitly points to estimate_rent for that need. It stops short of explicitly naming the alternative tool or stating when-not to use this one, so guideance is clear but not fully prescriptive.

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