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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, non-open-world), so the description's added value is the pricing model (free vs priced OS AddressBase-backed siblings) and the UK-only geographic scope. These are genuinely useful behaviors not in the annotations, though pagination/rate behavior is left unstated.

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 purpose in the first sentence, then routing and pricing in short scannable blocks. Slightly padding with the closing 'UK only. Free.' fragments that restate earlier points, but nothing significant is wasted.

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 need not be described, and annotations cover safety. The description supplies scope, pricing, and sibling routing, leaving only parameter details thin — a minor gap for a low-complexity single-required-param search 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 description coverage is 0% for three parameters, so the description must compensate. It only partially does: 'partial address or postcode' hints at the q input format and 'UK only' implicitly bounds country, but max_results is never explained and no value ranges or defaults are given.

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 ('Returns ranked candidates for a partial address or postcode') and immediately distinguishes itself from address_resolve by naming what that sibling does instead. An agent can tell it apart from address_by_postcode/address_by_uprn 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?

Explicit routing: use address_resolve to canonicalize a candidate, and 'Prefer it for anything interactive, and resolve once at the end' gives a clear when-to-use pattern. It also names when competitors are preferred (priced lookups vs free narrowing).

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