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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely non-redundant context: coverage (~60 countries) and the paid model ($0.002 USDC per call via x402), which an agent needs to know before invoking. It still omits what happens on partial input or how results are shaped, so not 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?

A single dense sentence that front-loads the resource, enumerates the two lookup modes, and appends cost last. No filler, no restatement of the name.

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?

No output schema and no parameter documentation mean the description must explain inputs and returns, and it only covers the two modes plus cost. An agent still cannot tell which parameters to supply for a successful call or what a result contains, which is a meaningful gap for a 4-parameter tool.

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 0% and all four parameters (city, code, state, country) are undocumented and optional, so the description carries the burden. It implies code drives the forward mode and city drives reverse, with state/country as filters, but never states which combination is valid or that nothing is required. Partial compensation only.

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?

States a specific verb+resource ('postal and ZIP code lookup') and clarifies both directions of the operation: code-to-places/state/coordinates and city-to-codes. However, it never differentiates itself from the sibling 'zip' tool, which appears to cover the same territory, so an agent cannot tell them apart without opening schemas.

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 two modes (forward lookup by code, reverse lookup by city) imply when each parameter set is relevant, which is useful implicit guidance. But there is no explicit when-to-use versus 'zip', 'geocode', or 'address_validate', and no statement of which parameters are required for which mode.

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