Look up a postal code. Returns the places (city, state/region, latitude/longitude) matching the given postal code in the given country. Returns: Matching places with coordinates for the postal code..
| Name | Required | Description | Default |
|---|---|---|---|
| country | Yes | Two-letter lowercase country code, e.g. us, de, fr. | |
| postalCode | Yes | Postal / ZIP code to look up, e.g. 90210. |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and destructiveHint=false, so the agent knows this is a safe read operation. The description adds value by stating the return type (places with city, state/region, latitude/longitude). It does not disclose edge cases such as no match or multiple matches, but for a simple lookup with annotation coverage, this is acceptable.
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 short but contains redundancy: the first sentence says 'Returns the places...' and then a separate 'Returns: Matching places...' repeats similar information. There is also a typo with a double period. It could be condensed to a single clean sentence, so a score of 3 reflects the unnecessary repetition.
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?
This is a simple tool with two required parameters and no output schema. The description explains the return value (places with coordinates) and the input requirements, which is sufficient for a basic lookup. It could mention behavior on no match or multiple matches, but those are minor and not critical given the tool's simplicity.
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?
The schema provides 100% coverage for both parameters, including a pattern for 'country' and an example for 'postalCode'. The description only restates 'given postal code' and 'given country' without adding new format or semantic details. Baseline 3 is appropriate when the schema does the heavy lifting.
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 verb 'Look up' and the resource 'postal code', and explains the outcome: returns matching places with coordinates in the given country. Since there are no sibling tools, no differentiation is needed. This is a specific, unambiguous purpose.
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 clear context: use this tool to look up a postal code in a given country and receive matching places. It implies the appropriate usage but does not explicitly discuss when not to use it or mention alternatives. However, with no sibling tools, the absence of alternatives is not a gap.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Add one secure layer between your agents and this server.
With only one tool, there is no possibility of confusion or overlap. The tool's purpose is clear and singular.
The single tool follows a clear verb_noun convention ('lookup_postal_code'), which is consistent even though there is no other tool to compare against.
At one tool, the server feels thin for a domain like postal codes, which typically would benefit from additional operations like validation or listing supported countries. However, the singular lookup tool does cover the core function.
The server only supports lookup by postal code and country, but offers no way to list supported countries or validate a code. This is a significant gap for an agent needing to know the valid inputs, so the surface is incomplete.