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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds genuinely useful context beyond that: the cost model (2 credits / 2p, free on marketcode.ai). It does not disclose any cap on the number of addresses returned for large postcodes, nor behavior when the postcode is unknown or non-UK.

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 short sentences, each earning its place: the first defines the operation and scope, the second discloses cost. Front-loaded and free of filler.

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 and annotations cover the safety profile, so the description needn't restate return values. However, for a bulk-lookup tool it should mention practical limits (how many addresses are returned, whether there is pagination/truncation) and accepted postcode formatting, which are the main failure modes an agent would hit.

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 for the single required parameter. It only asserts 'UK postcode', which essentially restates the parameter name 'Postcode' — no guidance on case, spacing, or whether outward codes alone are accepted. It does not compensate for the coverage 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 verb+resource+scope: 'Return all addresses at a UK postcode.' The 'at a UK postcode' qualifier implicitly distinguishes it from address_by_uprn (addresses for one property) and address_autocomplete (partial string lookup), though no sibling is named.

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 usage is implied by the purpose statement — you call this when you already have a full postcode and want the addresses on it. But nothing states when to prefer address_by_uprn, when to use address_autocomplete to resolve a partial postcode first, or what to do if the postcode is invalid. Adequate but leaves routing to inference.

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