lookup_postal_code

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

The readOnlyHint annotation is present, and the description adds valuable behavioral context beyond it: description of multi-place postal codes, retourning all matches, and the error dict behavior (never raises). These are non-obvious behaviors that help the agent anticipate outcomes.

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 well-structured and front-loaded with purpose, followed by usage exclusions and behavioral edge cases. Every sentence adds distinct value, with no redundancy or 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?

Given the tool's moderate complexity (2 params, multiple return possibilities), the description covers purpose, parameter formats, usage exclusions, edge cases, and error behavior. It provides a complete picture even without an output schema.

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%, but the description fully compensates by explaining both parameters: country_code as a 2-letter ISO code with examples, and postal_code with country-specific format examples. This provides essential semantic detail missing from 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 uses a specific verb ('Resolve') and clearly identifies the resource (postal/ZIP code to place names, state/region, coordinates). It distinguishes itself from reverse lookups and full street address lookup, making the tool's purpose unambiguous.

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 provides explicit when-to-use examples ('what city is ZIP 90210 in') and states what it is not for ('not for the reverse... or for full street address lookup'). This clearly guides an agent on when to select this tool over alternatives.

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