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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so the safety profile is fully covered. The description adds that results derive from NEC Chapter 9 Tables 1, 4 and 5, which is genuinely useful provenance, but it says nothing about return shape, rounding, or edge behavior (e.g., overfill 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?

A single dense sentence that leads with the computed values and follows with the qualifying constraints; no filler, no repetition of the title.

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 a full output schema, complete parameter documentation and safety annotations, the description only needs to frame scope, which it does. The remaining gap is minor: it never states that mixed conductor sizes are unsupported in so many words, relying on "of one size."

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 three of four parameters carry enums with per-value explanations, so the schema does the heavy lifting. The description only restates the material scope (THHN/THWN-2, EMT/PVC-40) already encoded in the enums, adding no format or default guidance beyond it.

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 outputs (percent fill and maximum conductor count) and constrains the inputs (THHN/THWN-2, single size, EMT or PVC Schedule 40), which separates it cleanly from siblings like box_fill, wire_size and nec_ampacity. It lacks an explicit verb ("calculates") and never names a sibling to avoid, so it stops just short of a 5.

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?

There is no explicit when/when-not statement or alternative named, but the phrase "of one size" implicitly excludes mixed-size conductor runs, which is the main misuse case. Usage is inferable from the scoping rather than stated, so it stays at minimum-viable.

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