postal_code

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

With no annotations provided, the description carries the full burden and delivers real operational context: pricing ($0.0025 USDC per call), p99 latency (1500ms), coverage scope (70 countries), and a resolution limitation for GB, CA and IE. It does not describe error behavior, auth requirements, or rate limiting, which keeps it short of a 5.

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 well front-loaded: identity and modes first, then the GB/CA/IE caveat, then a compact Params/Cost/Latency block. The Params sentence partially restates the schema, but the cost and latency details justify their space in a paid API context.

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 4-parameter, single-purpose lookup with no output schema and no annotations, the entry covers identifiers, both modes, the required parameter, the partial-resolution caveat, price and latency. The main gap is a brief indication of the response shape (fields returned per mode), which the description only implies.

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 only 50%, so the description must compensate, and it does: it labels country as ISO2 and required, notes state is a state abbreviation with examples (CA, BY), and clarifies that city pairs with state. This adds meaning beyond the partially documented schema, though it never states that postal_code and city/state are mutually exclusive alternatives.

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 states a specific verb and resource ('Postal Code Lookup') and immediately defines both operating modes: postal code → place names/state/coordinates, and city + state → all postal codes. It also names the data source (GeoNames via zippopotam.us) and coverage (70 countries), so an agent can distinguish it from siblings like geocode without opening the schema.

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?

It explains which parameter combinations drive which mode (country + postal_code, or city + state) and states the GB/CA/IE outward-only restriction, which is genuine when-to-expect-limits guidance. It does not, however, contrast itself with sibling geo tools such as geocode or timezone, so there is no explicit when-not guidance.

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