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

Annotations already declare readOnly/idempotent/closed-world, and the description correctly adds things annotations cannot express: it is always paid (members only), $0.50 per calculation in USDC via x402, no free allowance, and a 50-item list is charged per item under one payment. It also discloses provenance behaviour (IEC 60287-1-1, IEC 60502-2) and that unsourced values are reported as missing. It stops short of describing failure/error behaviour.

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 purpose and value list are front-loaded and earn their place, and the payment sentence is essential. But the block repeating 'input: {freq: 50 | 60, trefoilMm?, flatMm?} (axis spacing, mm; absent: touching)' duplicates the schema description word for word and could be dropped, and the pricing detail is told twice.

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 six optional, deeply nested parameters and no output schema, the description does carry a lot: what values come back, that each carries a source, that gaps are flagged missing, and the full billing model. It is weaker on the shape of the response (no structure, units or nesting described) and on the alternative spec/design inputs, which an agent must learn from design_cable.

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 baseline is 3. The description restates the input object verbatim from the schema (freq, trefoilMm, flatMm, 'absent: touching') rather than adding new meaning, and it says nothing about the lang, spec or design parameters. Its only extra signal is that items are always returned in full and billed per item.

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?

The description states a concrete deliverable and enumerates it: capacitance, charging current, inductive reactance (trefoil/flat), a.c. resistance with skin and proximity effects, dielectric loss and impulse levels, each with its source and explicit gaps where no source exists. That is far more specific than a restated title. It does not, however, say in one line how it differs from the closest sibling (design_cable), which it references only as the source of the input format.

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 implies usage by explaining the three alternative input forms (sentence, spec, design) and the batch form (items, up to 50), and points at design_cable for the spec/design shape. But there is no explicit when-to-use-this-versus-that guidance against siblings like check_cable, design_cable or economic_size, so the agent must infer the routing.

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