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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=true, and destructiveHint=false, covering the safety profile. The description adds a behavioral caveat not visible in the schema or annotations: demo mode restricts accepted values to selected sample FIPS codes. This is useful, though it remains slightly vague about what happens for non-sample FIPS values.

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?

Two short sentences with no filler. The core behavior is front-loaded ('Return ZIP profiles in a county by county FIPS'), and the caveat about demo mode is added as a single additional sentence. Every word earns its place.

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, single-parameter, read-only lookup, the description is largely complete: it states the input, the output concept, and the demo-mode limitation. The lack of an output schema means 'ZIP profiles' is not expanded into specific fields, but the tool is simple enough that this is a minor gap rather than a serious omission.

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 already fully documents the single fips parameter with a type, description, and example ('13121'), so the baseline is 3. The description reinforces the county-FIPS concept and adds the demo-mode sample restriction, but it does not add substantial new parameter semantics beyond the schema.

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 action ('Return'), a specific resource ('ZIP profiles'), and the key input ('county by county FIPS'). This clearly distinguishes it from sibling tools like geo_zip_lookup, which operate on a single ZIP code rather than a county.

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 makes the usage context clear: use this tool when you have a county FIPS and want the ZIP profiles contained in that county. It does not explicitly name alternatives or exclusion conditions, so it falls short of a 5, but the intended use is unambiguous enough for an agent to route correctly.

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