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 context beyond that: the data provenance and vintage (EPA SDWIS, 2026 Q3 snapshot) and the aggregation scope, which tells the agent results are a point-in-time rollup rather than live data. It does not discuss pagination or result size, but for a single-state aggregate that is a minor gap.

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 metric list is front-loaded and every clause names a distinct returned field, so the length is largely earned. The single long sentence is dense but readable; a bulleted or split structure would scan slightly faster.

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?

There is no output schema, so the description carries the burden of describing return values, and it does so thoroughly by enumerating each aggregate metric. Combined with the data source and the sibling routing, an agent has everything needed to select and call this tool 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?

Schema coverage is 100% and the single parameter already documents the two-letter state code format. The description reinforces the state-level scope ('a whole US state') but adds no format or validation detail 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 verb (summarize) and resource (public water systems for a whole US state), then enumerates the exact metrics returned: system counts, population served, health-based violations, top counties, and UCMR5 PFAS coverage. This is clearly distinguishable from the county-level and per-system siblings.

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?

Explicitly routes the agent: 'Use get_county_water_summary instead for one county, and search_water_systems to find individual systems in the state.' Both the alternative and the selecting condition are named, leaving nothing to inference.

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