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

Annotations cover the safety profile (readOnly, idempotent, destructive=false, openWorld=false), so the bar is lower, and the description goes well beyond them: it discloses that raw samples are unpublished, that UCMR 5 results are entry-point monitoring rather than compliance determinations or tap results, that the May 2026 rescission documents are proposals, and that name-withheld systems are keyed by PWSID/city. These are real interpretation caveats, not restatements.

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, then one long but dense enumeration of contents followed by the caveats. Nothing is redundant, though the second sentence is heavily loaded and could be split for readability.

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 must carry the return-shape burden — and it does, enumerating sampling locations, sample events, dates, complete-set averages in ppt, per-chemical counts, Hazard Index, the six flags, the six 2024 rule records with status history, file hashes, and caveats. An agent knows exactly what it will receive.

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 the single pwsid parameter already documents the 9-character EPA ID with an example. The description only echoes 'by PWSID' with no added syntax or format detail, 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?

Opens with a specific verb+resource+scope: 'Returns one public water system's full record in the MORVS PFAS Drinking-Water Register by PWSID.' The word 'full' distinguishes it from the sibling pfas_system_lookup without needing to name it, and the enumerated contents make the deliverable unambiguous.

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 is implied by 'full record ... by PWSID' (reach for this when you want everything about one system rather than a search), but the description never states when to prefer it over pfas_system_lookup or pfas_rule_impact, nor any prerequisites. Adequate context, no explicit alternatives or exclusions.

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