v1_zipPostal code lookup: ZIP/postal code → place(s) & coordinates. Source: Zippopotam.us. $0.005 per call · GET /v1/zip
| Name | Required | Description | Default |
|---|---|---|---|
| code | Yes | Postal code. Example: '90210'. | |
| country | No | ISO-3166 alpha-2 (default US). Example: 'US'. |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish read-only and non-destructive behavior. The description adds valuable context: the external source (Zippopotam.us), per-call cost ($0.005), and the GET endpoint, which are useful operational details beyond the annotations.
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 compact line that front-loads the purpose and then adds source, pricing, and endpoint information efficiently. Every element earns its place, with no redundancy.
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 read-only postal code lookup, this is complete: it states the input, output, data source, cost, and HTTP method. Annotations cover safety, and the output 'place(s) & coordinates' is sufficient 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?
Schema description coverage is 100%, so the schema already documents both 'code' and 'country'. The description does not add extra meaning about either parameter beyond what the schema provides.
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 'Postal code lookup' and clearly specifies the transformation '(ZIP/postal code → place(s) & coordinates)', making the tool's purpose obvious. It also distinguishes itself from sibling tools like v1_reverse_geocode (coordinates → place) by showing input and output.
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 arrow implies when to use the tool: when you have a postal code and need places or coordinates. However, it does not explicitly mention alternatives such as v1_geocode or v1_reverse_geocode, nor does it state when not to use this tool.
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.
Every tool targets a distinct resource or operation—geocoding, weather, DNS, VIN, stock quotes, etc.—with no meaningful overlap in purpose. Even the location- and finance-related tools are clearly separated by their descriptions.
All tools follow the same v1_<resource>[_modifier] snake_case pattern, such as v1_air_quality, v1_reverse_geocode, and v1_validate_email. Although the names are not verb-based, the convention is perfectly consistent across all 31 tools.
31 tools exceeds the 25+ threshold and creates a heavy selection burden for agents, even though the server's stated purpose is broad. Many endpoints are small single-purpose lookups that could be grouped into fewer combined tools without losing clarity.
As a general public-data utility, the set covers a wide range of common lookup categories: location, weather, finance, legal, health, business, internet, and reference data. It has minor gaps like historical financial time series or phone-number validation, but no obvious dead ends since all tools are self-contained read-only lookups.