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

Annotations already cover readOnly/idempotent/non-destructive, and the description adds genuinely new behavior: per-item outcome codes (ok | no_lease | not_found | error) returned in input order, and a billing model ('charged per property answered — the sum of the single calls, never more'). Partial-failure and cost behavior are the things an agent most needs and neither is in the structured data.

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?

Four compact sentences with no filler; the batch scope and per-item outcome contract are front-loaded, followed by coverage, cost, and the key-acquisition path. Every clause carries actionable information.

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, yet the description still supplies the outcome vocabulary and ordering guarantee plus coverage limits and cost — everything needed to call it correctly and interpret partial results. Nothing material is missing for a one-parameter batch tool.

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 0% for the single `uprns` array parameter, so the description must compensate — and it does by explaining the identifier type (UPRN, not an address), the batch cardinality (up to 100), and how to obtain a valid value via `address_resolve`. It stops short of stating the element type/format explicitly, leaving a small gap.

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 operation (registered lease lookup) with an explicit batch scope of up to 100 properties in one call, and names the single-item sibling `property_lease` it mirrors. An agent can distinguish it from the ~90 siblings 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?

Explicitly names the prerequisite alternatives and the routing condition: call `address_autocomplete` (free) to narrow, then `address_resolve` to get a UPRN. Also states the geographic restriction (UK only) and that the key is a UPRN rather than an address, which is exactly the when/how-not guidance needed.

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