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

Annotations already declare readOnly, idempotent, non-destructive, open-world, so the safety profile is covered. The description adds genuinely useful behavioral context beyond them: the catalog is a fixed set of ~76 entries and coverage is limited to fluids with 'full thermophysical property surfaces', warning the agent that a name it expects may be absent.

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?

Two sentences, front-loaded with the verb and scope, with the catalog contents packed into a single parenthetical rather than a bulleted list. Nothing is padding.

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?

For a one-optional-param read-only listing with full annotation coverage and no output schema, the description is nearly complete. The remaining gap is that it doesn't say whether the returned names are the exact identifiers to pass into nist_fluid_properties, which is the main thing an agent needs to chain these calls.

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 the single 'query' parameter and its omit-to-list-all behavior. The description echoes that with 'substring of the name or refrigerant code', which only marginally extends the schema by hinting that codes like 'R1' match. 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?

Specific verb + resource ('List the ~76 fluids') with an explicit scope and an enumeration of the catalog's contents (water, nitrogen, refrigerants R11-RC318, etc.), which tells an agent exactly what universe of data this covers. It does not name the siblings nist_fluid_properties or nist_fluid_saturation, so the distinction between this index tool and the property-lookup tools must be inferred from the phrase 'full thermophysical property surfaces'.

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?

It handles parameter usage well ('Omit to list all fluids'), implying this is the discovery step before a property lookup, but it never states when to call this versus nist_fluid_properties or nist_fluid_saturation. The workflow guidance is implied rather than explicit.

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