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 needs no repeating. The description adds genuinely useful behavior beyond that: the property set returned, that phase (liquid/vapor/supercritical) is reported, and that every value carries its unit — valuable since there is no output schema.

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 long property enumeration is front-loaded and earns its place because no output schema exists to convey the return shape. The trailing routing sentence is short and actionable. Slightly dense but no filler.

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 returned properties and the unit guarantee. Coverage of fluid scope (~76 fluids, examples given) plus the list-tool fallback makes it callable with confidence. It stops short of describing behavior at saturation boundaries, which is the one omission an agent could stumble on.

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 includes an example plus enums with stated defaults, so the schema fully documents all five parameters. The description only restates that evaluation happens 'at a given temperature and pressure' and adds nothing about units or defaults beyond the schema. 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 specific verb (evaluate) and resource (thermophysical properties of a NIST reference fluid at T,P), and enumerates the exact returned quantities including phase. An agent can distinguish it from nist_fluid_list (coverage lookup) and nist_fluid_saturation (saturation states) without opening any schema.

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 routes the agent: 'Call nist_fluid_list first if unsure a fluid is covered.' However it never mentions nist_fluid_saturation, which is the obvious alternative when the state is on a saturation line rather than at arbitrary T,P — a meaningful gap in when-to-use guidance.

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