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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so safety is covered. The description adds genuinely useful context beyond them: the data provenance (ONS rents, HM Land Registry prices) and the monthly refresh cadence. It does not say what happens for an unmatched area name.

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?

Two sentences, no filler, and the core capability plus provenance is front-loaded before the usage branch. Every clause carries information an agent needs.

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 still tells the agent what comes back (average rent, average price, gross yield, plus national rank), where the data originates, and how to switch between lookup and ranking modes. Nothing essential for correct invocation is missing.

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%, so the baseline is 3, but the description adds cross-parameter behavior the schema does not: 'area' switches between single-area lookup and ranking mode, and 'region'/'limit' are effectively ranking-only modifiers. That linking of parameters to output modes is real added 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?

States a specific verb and resource ('looks up average rent, average price and gross rental yield for local authority areas in England and Wales') with named data sources and coverage. It is unambiguously distinct from the sibling calculators (calculate_stamp_duty, calculate_btl_mortgage) because it is a data lookup/ranking tool, not a computation.

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 explicitly branches usage: pass an area name for that area's figures and national rank, or omit it to get the highest-yielding areas, optionally narrowed by region. That gives clear when-to-use-per-mode guidance, though it names no alternative sibling tools for related questions.

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