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

With no annotations provided, the description carries full weight and does so excellently. It discloses the full return shape, the verification statuses, and the critical conflict-handling rule: never pick a conflicting code silently, tell the user both. This goes well beyond the structured schema.

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 dense but front-loaded with the main purpose. The long second sentence enumerates return fields that are necessary because no output schema exists. Every clause earns its place, though it could be slightly better organized.

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 tool with two simple parameters, no output schema, and no annotations, the description is remarkably complete. It explains the geographic coverage, the structure of results, data provenance, verification semantics, and how to handle conflicts. Nothing essential is missing for correct invocation.

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 100%, so the baseline is 3. The description adds minor value by explaining 'US ZIP code' and giving examples like '75001' and '16000', but the schema already documents both parameters clearly and completely.

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 opens with a specific verb and resource: 'Look up a postal code or US ZIP code.' It clearly defines what is returned and is unambiguous against sibling tools like area_code_lookup and nearby_places, even without naming them.

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 clearly implies when to use the tool: whenever a postal/ZIP code needs resolving for the listed countries. However, it does not explicitly state when not to use it, nor does it name alternatives such as area_code_lookup for telephone area codes.

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