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

Goes well beyond the readOnly/idempotent/openWorld annotations: it discloses the commercial model ('Always paid: the site gives it to members only', '$0.50 per calculation in USDC with x402; no free allowance', per-item billing for lists up to 50), and states the substantive caveat that it never asserts interchangeability. It also says each value carries its source and 'seen level', which no structured field conveys.

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?

Front-loaded with the purpose and the sibling contrast, but the body is one densely nested paragraph of table citations (UL 44, UL 83, UL 1072, IEC 60502-1 Table 15, UL 1581 Tables 50.231 and 50.182) that a selecting agent does not need. The implementation path 'server/pro/equivalence.ts' is noise for tool invocation.

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 parameters, nested objects and no output schema, the description compensates by describing the return shape (lines plus a Markdown/txt report file) and the payment flow. The only gap is that it never clarifies the mutual exclusivity of sentence vs spec vs design vs items on the input side.

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 coverage is 100%, so the schema already defines lang, spec, design, sentence, input and items. The description adds only marginal meaning beyond it — the per-item price for lists and the format enum mirrored from the schema — and never explains how sentence/spec/design relate as alternatives.

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 and resource with scope: an IEC power cable in mm² compared against its North American counterpart 'value by value', returned 'as lines and as the report file (Markdown or plain text)'. It explicitly demarcates itself from the closest sibling: find_equivalents is 'a quick verdict across many countries' standards', while this is 'the one IEC to NEC / UL pair, value by value'.

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 an explicit alternative and the condition that selects it ('For a quick verdict across many countries' standards use find_equivalents (cheaper...)'), plus the domain of use ('for bids', 'a member downloads it under the equivalents panel'). It also warns the buyer's specification decides, which frames when the output should not be used.

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