ZIP Code Lookup

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

Annotations indicate readOnly, idempotent, and non-destructive behavior, which the description aligns with. The description adds context by detailing the return fields (city, region, country, codes, coordinates) beyond annotations, but does not mention edge cases or 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 sentences, succinctly covering purpose and optional filter. No redundant or extraneous information.

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?

For a simple lookup tool without output schema, the description adequately explains what is returned. It could be improved by specifying the response structure (e.g., object containing keys like city, region, etc.) but overall covers essential behavior.

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% but the description adds value by providing examples for 'code' (e.g., '10009', 'SW1A 1AA') and explaining that 'country' is an ISO 3166-1 alpha-2 code that narrows the search. This supplements the schema.

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 looks up a single ZIP or postal code and specifies the returned data (city, region, country, codes, coordinates). It distinguishes from siblings like zipcode_bulk_lookup by emphasizing 'single' and from zipcode_by_city or zipcode_by_region by the lookup method.

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 single code lookup but does not explicitly compare with alternatives (e.g., zipcode_bulk_lookup for multiple codes, zipcode_by_city for city-based lookup). No when-to-use or when-not-to-use guidance is provided.

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