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

Annotations already declare readOnlyHint, idempotentHint and non-destructive, so the bar is lower. The description usefully adds that the result comes from a closed-form momentum plus blade-element model and requires no account or external service, telling the agent the output is deterministic and offline. It does not cover accuracy limits or validity ranges of the model, which would have pushed it to a 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?

Three short paragraphs, zero filler, and the output/scope statement is front-loaded before the input conventions. Every sentence carries distinct information.

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?

An output schema exists, so return values need no explanation, and the description fully covers what the tool is and the two most ambiguous inputs. The gap is that a majority of parameters, including the required rpm and the default-zero altitude_m and airspeed_m_s that govern the model's operating point, are left undocumented.

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 0% across 8 parameters, so the description carries the full burden. It does well for two: the 10x5 -> diameter_in/pitch_in example clarifies the printed-size convention, and chord_ratio gets a definition plus four concrete recommended values. The other six (rpm, blades, altitude_m, camber_pct, airspeed_m_s) are never mentioned, leaving the required rpm and the static-vs-forward-flight meaning of airspeed_m_s entirely to inference.

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-and-resource statement ('Thrust, torque and shaft power for one propeller, from its printed size') that names the exact outputs. The 'no motor, no battery, no account' clause explicitly separates it from the powertrain simulation siblings, so an agent can route without opening a 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?

Gives clear selection context by excluding motor/battery/powertrain cases, which implicitly routes the agent to simulate_powertrain or sweep_powertrain for those. It does not name the alternative explicitly or state a positive 'use this when...' condition, so it falls just short of full routing guidance.

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