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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so safety is covered. The description adds genuinely new behavioural context the annotations cannot express: the 1-credit cost and the fact that several regions are gated behind a paid plan, which materially affects whether an agent should call it.

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 tight sentences, front-loaded with the purpose before the input requirements and the pricing caveat. The only waste is the redundant "Shoe Size Converter: Shoe Size Converter translates" 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?

For a three-parameter, read-only conversion tool with an output schema, it covers purpose, inputs, supported regions, and cost. The one ambiguity left is whether conversion targets are chosen implicitly and which gender values are valid, but nothing critical to calling it is missing.

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 does add one thing the schema lacks — an enumeration of valid source regions, since the `from` parameter has no enum — but it says nothing about accepted gender values or size formats, so the added meaning is modest.

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 uses a specific verb ("translates") plus a concrete resource ("footwear measurements across regional standards") and enumerates the supported systems, so it is distinguishable from near neighbours like RingSizeConverter or UnitConverter without opening the 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?

It tells the caller exactly what to supply ("a size, source region, and gender category") and states the free-tier boundary (European, Japanese, and centimeter output requires a paid plan). It does not name a sibling alternative or a when-not-to-use case, which keeps it off a 5.

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