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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuinely new behavior: a 20-name cap and mixed-script look-alike warnings, which an agent could not infer from the schema or annotations. It stops short of saying what a partially-invalid batch returns or how warnings are surfaced.

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 sentence with no filler, front-loading the core conversion purpose and appending scope and safety notes in priority order. Every clause (bidirectionality, batch limit, look-alike warning) contributes distinct information.

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 only two parameters and no nested objects the surface is small, and the annotations carry the safety profile. However there is no output schema, and the description never indicates the return shape (mapped pairs? array of converted strings? where warnings appear), leaving a real gap for an agent that must interpret results.

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; both parameters and the direction enum are already documented in the schema. The description only restates the Unicode/Punycode direction concept and the 20-item limit, adding no syntax, normalization, or error semantics beyond structured data.

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 (converts) and resource (international domain names) with the exact bidirectional scope 'between Unicode and Punycode (xn--)' and an added safety behavior (mixed-script look-alike warnings). No sibling (dig, dns_lookup, domain_name_ideas) performs IDN transcoding, so an agent can immediately route IDN encoding/decoding here.

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 naming the input form and a batch ceiling, but never states when to choose this over alternatives or how the batch/warning behaviors should influence a decision. The phrase 'one name at a time, up to 20 names' is also internally ambiguous for an array-valued parameter, leaving the agent to reconcile the constraint itself.

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