engineering.sn_fatigue_life

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

Annotations already declare this a pure, idempotent, closed-world read. The description adds genuinely non-obvious behavior: the 30-significant-digit power evaluation and the deliberate omission of mean-stress correction and fatigue limit, which materially affect result interpretation. It stops short of describing the return payload or how the exponent sign interacts with error cases.

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 formula and the cycles-vs-reversals distinction are front-loaded, then constraints, then scope limits in a tight sequence with no filler. It is dense but every clause carries information; readability suffers slightly from packing four distinct concerns into one paragraph.

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 here. For a three-input closed-form calculation, the description covers the governing equation, unit and sign preconditions, the reversals-versus-cycles distinction, numerical precision, and the physical effects deliberately excluded — everything an agent needs to call it correctly and to know when not to.

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?

With 0% schema description coverage the description must carry the load, and it does: all three parameters get unit requirements (stress_amplitude and fatigue_strength_coeff in the same stress unit, both > 0) and a sign plus typical range for basquin_exponent. The one unaddressed oddity is that all three are typed as strings while the math implies decimal values, which the description never explains.

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?

Names the exact physical model (Basquin S-N), gives both the forward and inverted form, and states the computed quantity is cycles to failure rather than reversals. The clarification that N_f is cycles, not 2N_f, removes the single most common ambiguity in this calculation and separates it from siblings like bearing_life_l10 or weibull_reliability that also return 'life'.

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?

Applicability is stated through constraints (positive, unit-matched stress values; negative exponent typically -0.05 to -0.12) and through explicit exclusions: mean-stress correction and the fatigue limit are not modeled, which tells the agent when this tool is the wrong choice. It does not name an alternative tool for those cases, so it falls 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.