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

Annotations already establish a safe, idempotent, closed-world read; the description goes further by disclosing the EPA Table 4 method, the method version, that counts cover every matching system while only `limit` systems are listed, and that outputs are not compliance determinations (not_compliance: true). It does not describe pagination or the exact record shape, but it adds genuine behavioral context beyond the annotations.

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 purpose is front-loaded correctly, but the remainder is a single dense sentence with nested parentheticals and a long comma-chained list of return contents. Every clause carries information, yet the structure makes it harder to parse than it needs to be.

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 carries the full burden of describing returns, and it does so thoroughly: status label, system and population counts, PWSIDs flagged for rescission, largest systems by population, register-published figures, and method version. Combined with the scenario definitions and the not-compliance caveat, an agent has everything needed to call and interpret this tool.

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%, so the schema already documents all five parameters including enum meanings and the default/max for `limit`. The description's phrase 'optionally filtered by state file, owner type and minimum population' restates the schema rather than adding syntax or interpretation, so the baseline of 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 names a specific verb (compares) and resource (two rule scenarios in the MORVS PFAS Drinking-Water Register) and defines each scenario's contents precisely. It is clearly a different operation from per-system siblings like pfas_system_lookup and pfas_system_history, though it never names them explicitly.

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?

Usage context is implied by the scenario definitions and the caveat that results are monitoring comparisons rather than compliance results, but there is no explicit statement of when to choose this tool over pfas_system_history or pfas_system_lookup, and no prerequisites are given.

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