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

Annotations already establish readOnlyHint=true, openWorldHint=true, and destructiveHint=false, so safety is covered. The description goes beyond them usefully by disclosing that the free result set is limited to three fields, that paid tiers return additional fields, and that each call costs 10 credits — a real constraint an agent should know before invoking. It does not explain failure behavior for unmatched county names, keeping it off 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?

It is short and the core capability is front-loaded, and the credit cost is sensibly placed at the end. However, the opening redundantly repeats the tool name twice ('County Data Lookup: County Data Lookup is a county lookup API'), which is pure filler in an otherwise tight two-sentence definition.

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?

With an output schema present, the description needn't explain return structure, and both required parameters are fully documented. The tier note is the genuinely necessary piece of context, since it explains why some expected fields may be absent from a response. Additional detail on invalid-input behavior would be the only remaining gap.

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 100% and both parameters carry their own descriptions with examples (MO, Jackson), so the schema does the heavy lifting. The description only restates that lookup is by state and county name, adding no format, casing, or disambiguation detail beyond what the schema already says. 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?

The description gives a specific verb and resource: retrieves income, poverty rate, and life expectancy for any US county, keyed by state and county name. That is clear enough to distinguish it from generic geography tools, but it never names or contrasts with nearby siblings such as PopulationData, ZIPDemographics, or CostofLiving, so the agent must infer the boundary itself.

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 or when-not-to-use guidance and no named alternative tool for overlapping data (demographics, cost of living, income). The only conditional statement is a tier note that paid plans unlock extra fields, which informs expectations about coverage but does not tell the agent how to choose this tool over a sibling.

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