validate_postcode

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

Discloses deterministic format check only, no lookup, and return format. However, does not specify behavior on invalid input (error or response).

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 concise sentences, imperative tone, no redundancy.

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?

Covers purpose, input, behavior, and return structure well for a single-parameter tool, but lacks details on invalid input handling.

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?

Adds significant meaning beyond schema: UK postcode, well-formed, splitting, canonical spaced form. Schema just says 'UK postcode to validate'.

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?

Clearly states it validates a UK postcode and splits it into outward/inward codes, distinguishing it from the sibling tool which is about flood risk.

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 tells when to use ('before storing or matching') and what it doesn't do ('no lookup'), but lacks explicit alternatives or when not to use.

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