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

Annotations only establish that this is a safe read (readOnlyHint, idempotentHint, openWorldHint=false), but the description adds substantial context beyond them: it is offline and instant with no DNS/registry/network call, and it discloses a real limitation — it catches script tricks only, not typo or digit swaps (paypa1.com), so a clean result does not mean the domain is safe. This is unusually rich behavioral disclosure.

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 definition and example, then usage/routing, then behavior and limitations. Every sentence earns its place; no filler or restatement 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 single-parameter, offline, read-only tool with an output schema already covering return values, the description supplies the remaining essentials: scope of detection, negative-result caveat, and sibling routing. Nothing needed to call it correctly 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% and the schema already documents the single 'name' parameter including the Unicode/punycode formats and the rejection of full URLs. The description contributes only an illustrative example, so it neither extends nor contradicts the schema — the baseline 3 for a fully covered parameter is appropriate.

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 (check a domain/Web3 name for visual look-alike/homograph) and defines the concept concretely with a worked example ('раураl.com reads as paypal.com'). An agent can distinguish it from lookup_target and the other siblings without opening any 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?

Gives explicit use cases (phishing triage, brand monitoring, screening candidate or incoming names) and an explicit alternative with a routing rule: lookup_target already includes this warning, so don't call both for one name. That is exactly when-to-use plus when-not-to-use guidance.

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