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

With no annotations, the description carries the full burden and does disclose real behavior: one ZIP can map to several counties, the choice affects premium, and the resolved row must be propagated on every later request. It omits failure modes (unknown/non-US ZIP, invalid format handling) and whether results are cached or authoritative, so it stops short of full disclosure.

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?

Four sentences, front-loaded with the verb and return shape, then sequencing, then the multi-county caveat, then the handoff contract. Each sentence earns its place; the multi-county sentence is slightly long but carries the key decision logic.

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 exists, so the description must explain return values and it does (counties array, hasMultipleCounties), alongside ordering and the downstream location contract. An agent has everything needed to call it and use the result correctly.

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?

Only one parameter and the schema already documents it completely (pattern ^\d{5}$, example '64063'), so the baseline is 3. The description confirms '5-digit ZIP' and adds downstream usage context for the resolved values, but adds no new syntax or edge-case meaning for the input itself.

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 and resource ('Resolves a 5-digit ZIP') and enumerates the exact returned row shape (fipsCode, zipCode, countyName, state) plus the sibling `counties`/`hasMultipleCounties` wrapper. An agent can distinguish this lookup from quote_carriers and get_eligibility_questionnaires without opening a 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?

Gives explicit sequencing ('Call this FIRST before quoting'), explains the ambiguous multi-county case and the requirement that the applicant choose because premiums differ by county, and prescribes the downstream handoff format. Nothing about when or how to invoke it is left to inference.

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