Lookup UK Postcode

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

With no annotations provided, the description carries full burden for behavioral disclosure. It describes the input and output but does not mention error handling, rate limits, or authentication requirements. For a simple lookup, this is sufficient but not exemplary.

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 a single, well-structured sentence. It front-loads the conditional and lists the output comprehensively without any wasted words.

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?

The description covers the core functionality and lists the return fields, which compensates for the lack of an output schema. It omits error handling and response format, but for a one-parameter tool this is reasonably complete.

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 100%, and the parameter's schema already includes a description. The tool description does not add significant semantic value beyond the schema—it simply restates 'Given a UK postcode'. Thus, baseline score of 3 applies.

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 clearly states the tool's purpose: given a UK postcode, return delivery points from Royal Mail PAF. It uses specific verbs and lists the exact data returned (street, house number, etc.), distinguishing it from sibling tools like geocode or validate_address.

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 description implies when to use the tool (when you have a UK postcode and want delivery points), but it does not explicitly state when not to use it or compare it to siblings (geocode, reverse_geocode, validate_address). The guidance is adequate but lacks explicit differentiation.

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