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

Annotations already cover readOnly, idempotent, non-destructive, openWorld, so the description is not obligated to restate safety. It adds genuinely useful behavior: the coverage-window limitation tied to ingredients_since, and the found:false semantics for a valid-but-absent CAS number. No auth or rate-limit context, keeping it below 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?

One dense paragraph, front-loaded with what the tool does before the return summary and the coverage caveat. Every sentence carries information, though the return-value enumeration is slightly bulky for a non-output-schema tool.

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 usefully enumerates what comes back (summary counts plus sample fields) and flags the coverage-window and found:false edge cases. Adequate for a read-only, 100%-schema-covered query tool, short only on pagination behavior across the limit/offset pair.

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 all four parameters are already documented in the schema. The description restates the CAS format example and the optional state scoping, which duplicates rather than extends the schema, and says nothing about limit/offset. 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 precise verb+resource: usage locations of a chemical in hydraulic fracturing jobs, keyed by CAS number, optionally state-scoped. The CAS-number framing and the explicit 'this pack's ingredients coverage window' scope separate it from sibling tools like frac_chemicals and frac_wells without needing to name them.

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?

Clearly establishes the use case (look up where a specific chemical appears by CAS number, optionally narrowed by state) and implicitly warns against expecting full FracFocus history. It does not explicitly name an alternative tool for the non-CAS-based or cross-chemical case, so the routing guidance stops short of a 5.

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