Look up the city and state associated with any US ZIP or postal code. Provide a postal code and optional country code to retrieve corresponding location data for address verification.
Look up city and state from a ZIP/postal code.
| Name | Required | Description | Default |
|---|---|---|---|
| countryCode | No | Country code (default: 'US') | |
| postalOrZip | Yes | ZIP or postal code to look up |
Changes observed during successful MCP inspections.
v1.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden, and it does disclose the core behavior: a lookup returning city and state. It does not mention edge cases such as invalid/unsupported postal codes, default country behavior (US is in the schema, not the description), or the exact output shape.
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 clear sentence with no filler. Every word contributes to the purpose, and the key object ('city and state') is front-loaded.
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 two-parameter lookup, the description and schema together are mostly sufficient, but there is no output schema and the description does not specify the return format or any country-specific behavior beyond the schema's default. It also lacks routing guidance to distinguish it from address verification tools.
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 schema already explains both postalOrZip and countryCode. The description adds little beyond the schema, except reinforcing that the postal code maps to a city/state result, which is consistent with the baseline.
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 ('look up') and names the exact resource ('city and state from a ZIP/postal code'), so an agent can tell this is a postal-code lookup. It does not explicitly differentiate it from the address verification siblings, but the operation is distinct enough on its own.
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?
No guidance is given about when to choose this tool over sibling tools like postgrid_verify_address or postgrid_autocomplete_address. The description states what the tool does but not when it is preferred or when it should be avoided.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.