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

No annotations are provided, so the description carries the full behavioral burden. It discloses that postcodes can span multiple towns, but omits auth/Pro requirements, read-only nature, output shape, rate limits, and error behavior.

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?

The description is two short sentences with no filler, and the multi-town caveat is useful. The leading 'PRO.' is ambiguous, but overall the text is appropriately sized and front-loaded.

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?

This is a two-parameter lookup with no annotations, no output schema, and only 50% schema coverage. The description explains result breadth but leaves auth requirements, return structure, and sibling selection unaddressed, so it is too thin for the tool's complexity.

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 50%: access_token is documented, but the required postcode parameter has no schema description. The description says 'for one postcode' but adds no format, syntax, or token semantics, so it fails to compensate for the undocumented required parameter.

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 it returns all address matches for a single postcode and notes that some postcodes span multiple towns. This clearly identifies the resource and scope, but it does not name or distinguish postal_lookup or batch_postal, so sibling differentiation is missing.

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?

There is no explicit when-to-use or when-not-to-use guidance. The only hint is 'all matches' and the multi-town caveat; it never directs agents to postal_lookup or batch_postal for alternative cases.

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