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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful behavior the annotations do not: the underlying data source (Census ACS), that output fields vary by plan tier (free vs paid), and that each call costs 10 credits — a material cost signal for an agent deciding whether to call it repeatedly.

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 body is compact and front-loads the data source and field tiers, but it wastes the opening on a redundant restatement of the title ('ZIP Demographics: ZIP Demographics is...'), and the credit cost is buried at the end in parentheses where it deserves more prominence.

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?

An output schema exists, so return-shape explanation is unnecessary, and the description covers source, tier-dependent fields and cost. For a single-parameter read-only lookup this is largely complete; only error behavior for invalid or non-US ZIPs and any rate limits are unaddressed.

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?

With a single parameter at 100% schema description coverage, the schema already documents the 'zip' string with a 90210 example. The description's phrase 'any US ZIP code' reinforces the format constraint but adds no syntax, normalization or invalid-input behavior beyond the schema, so the baseline 3 applies.

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 resource and scope: demographic data for any US ZIP code, sourced from the Census American Community Survey, and names the fields returned (population, median household income, plus age, income, education, housing, employment, race on paid plans). An agent can tell this apart from ZipCodesLookup or PopulationData by the field list, though the description never explicitly names those siblings as alternatives.

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 when-to-use or when-not-to-use guidance, and no alternatives are named despite near neighbors like ZipCodesLookup, PopulationData, CountyDataLookup and IPDemographics existing. The only implicit scoping is 'US ZIP code', which is scope rather than usage guidance.

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