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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds genuinely non-structured behavior: result ordering by gain, the commercial cost (40 credits / 40p) and the UK-only scope. It says nothing about pagination or the effect of the limit parameter, which keeps it short of a 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?

Front-loaded with the cohort definition, then a concrete illustrative output line, then the parameter note and hard constraints. Every sentence contributes something an agent would otherwise have to guess, with no padding.

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 shape needs no prose (the example is a bonus, not a substitute), and annotations cover safety. What remains thin is the tuning of `limit` and the thresholds behind min_years/min_gain_pct — for a 4-parameter query tool with 0% schema coverage, that keeps it at a 4 rather than a 5.

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 four parameters, so the description carries the burden. It does resolve the most error-prone one — `area_id` is the marts area id from `area_resolve` — and the cohort framing implicitly explains min_years (long-held) and min_gain_pct (high equity). `limit` and the actual defaults (10 years, 50%) are never mentioned, so compensation is partial.

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?

The description defines a precise cohort (long-held properties carrying a large paper gain, i.e. the off-market segment) and states the ordering rule explicitly: 'ordered by gain rather than by value.' That ordering detail alone separates it from the many sourcing_* and valuation_* siblings, so an agent can pick it without opening the 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 gives clear context signals — UK only, 40 credits, and that `area_id` must come from `area_resolve` — which is prerequisite guidance an agent needs. However, it never states when to prefer this over overlapping siblings such as sourcing_offmarket_owners or sourcing_owners, nor any exclusion beyond geography, so usage is implied rather than directed.

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