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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered. The description adds genuinely new context: figures come from a stored query against the source data, are dated with the measurement date, cost nothing and need no key — useful freshness and auth/cost disclosure beyond structured fields.

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?

Front-loaded with the core purpose and then a tight enumeration of the available figures, followed by provenance and cost facts. It is a single dense sentence with a long list, but every clause carries information; no filler or 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?

For a parameterless, read-only aggregator with no output schema, the description effectively substitutes for the return-value documentation by enumerating the categories of figures returned (counts, breakdowns, tables, ranked lists) and adds freshness and cost context. Nothing an agent needs before calling it is missing.

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 tool takes zero parameters, so per the rubric the baseline is 4. There is nothing for the description to clarify about inputs, and it correctly spends no words on them.

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 names a precise resource and scope: aggregate statistics about US ZIP Codes and Canadian postal codes, including counts, type/delivery-point/carrier-route breakdowns, per-state tables and ranked lists. This is clearly distinct from lookup-oriented siblings like zip_lookup or quick_zip, though it never names them, so differentiation is inferred rather than stated.

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?

There is no explicit when-to-use guidance and no mention of alternatives such as zip_lookup or quick_zip, which an agent must disambiguate against. The implied use case (wanted aggregate statistics rather than a single code's details) is left entirely to inference.

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