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 bar is lower. The description goes well beyond them with genuinely useful behavior: ONS Price Index validation each build, the ~few-points-a-year disagreement threshold, the rule that a missing recent month is a deliberate refusal rather than an outage ('say so'), and the caveat that `value` is an index level, never a rent. It stops short of describing pagination/limit behavior or smoothing effects, so not a full 5.

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?

Roughly 90 words, front-loaded with the identity and base period before the caveats and alternatives. Information-dense and mostly economical, though the em-dash clauses and semicolon fragments make it slightly harder to scan than it needs to be.

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?

An output schema exists, so return-format explanation is unnecessary, and the description supplies the crucial interpretive context (index level not a rent, refusal-vs-outage semantics, source validation). The only real shortfall is the unaddressed `method` parameter, which an agent must guess at when the default is unsuitable.

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 0% across 7 parameters, so the description carries the burden. It partially compensates by enumerating the geography options ('one postcode district, local authority or Great Britain') which map onto the area_type enum, and it references shared 'area and frequency rules'. However, hedonic_smoothed vs hedonic_raw is never explained, and start/end/limit formats are undocumented, leaving meaningful gaps.

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+resource ('Hedonic ASKING-RENT index for one postcode district, local authority or Great Britain'), its source (portal lettings), base period (2022M01 = 100), and outputs (bands and SEs). It explicitly contrasts itself with commercial_rent_index_series and asking_price_index_series, so an agent can route correctly without opening any 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?

Names the alternatives and their selecting conditions: commercial_rent_index_series is the commercial VOA series, and listing_market_series is the tool for rent LEVELS and yields. It also frames the use case as the residential asking-rent index specifically, leaving nothing to inference.

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