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

Annotations already declare a read-only, closed-world, non-destructive read, so the bar is lower; the description still adds real semantic context about aggregation breadth and the interpretive limit of the result. It gives no info on pagination or response shape (which matters since there is no output schema), keeping it below 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?

Front-loaded with the core purpose, followed by the metric list and then two scoping caveats. Dense but every clause carries information; the metric enumeration sentence is long but justified because no output schema exists.

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 no output schema, the description correctly compensates by enumerating the summary contents (counts, active count, population, health-based violations, worst-affected systems). Only gap is any hint about result format or whether zero-system counties return empty vs error.

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% with examples (IL, COOK), so baseline is 3; the description adds the non-obvious constraint that county names must be uppercase as reported to SDWIS, which prevents a common lookup failure. State parameter gets no extra guidance but the schema example suffices.

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?

Opens with a specific verb+resource ("Summarize public water systems serving a US county") and enumerates exactly which metrics are returned (system counts, population served, violation counts, worst-affected systems). This clearly distinguishes it from get_state_water_summary and get_water_system by scope.

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 bounds scope: a county summary covers every system serving any part of the county and is "not a verdict on the water system at a specific address" – implicitly routing address-specific questions to get_water_system. It does not name sibling tools directly or state when to prefer get_state_water_summary instead.

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