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

Annotations already declare readOnlyHint/idempotentHint/non-destructive, so the safety bar is lower. The description adds a genuinely non-obvious behavioral trait — sale and rental are aggregated separately, so median_asking_price and median_monthly_rent answer different questions — plus UK-only scope. That is real context beyond the structured fields.

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?

Front-loads the purpose in the first line, then adds the two nuances an agent would otherwise get wrong, then closes with scope constraints. No filler sentences.

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 values need no explanation, and the description pre-empts a likely misreading of the two median fields. It is nearly complete for a simple read-only lookup; the only gap is meaning for the limit/months controls.

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%, so the description carries the burden. It explains area_id's provenance well and the sale/rental distinction loosely maps to listing_type, but limit and months are left entirely undocumented. Partial compensation, so it lands at the minimum-viable 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 and resource: 'Which estate agents actually transact in an area, ranked by listing count.' The output ordering is even declared, which is unusual and helpful. This is distinguishable from siblings like market_ranking or actor_network without opening a 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?

It implies the prerequisite for area_id ('the marts area id from area_resolve') and scopes to 'UK only. Free.', which is useful context. But it never says when to reach for this versus alternatives (market_ranking, area_report), nor any exclusions — usage is only implied.

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