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

Annotations already declare readOnlyHint, openWorldHint and destructiveHint=false, so safety is covered. The description adds genuine behavioral context beyond that: the lookup is WHOIS-based, and it explicitly refuses to report an ambiguous status as 'registered' — an honesty/edge-case behavior an agent could not infer from structured fields.

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?

Purpose is front-loaded in the first clause and there is no filler. It is one long, slightly run-on sentence, but every clause adds a distinct fact (scope, method, ambiguity handling), so it is dense rather than bloated.

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 read-only lookup with no output schema, the description supplies the essentials: method, scope, and the three possible outcomes (verfügbar / bereits registriert / nicht eindeutig). It never describes the response shape or how errors are surfaced, which keeps it just short of complete.

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?

There is a single parameter with 100% schema description coverage ('Die zu prüfende Domain, z. B. example.de'), so the schema already carries the semantics. The description adds the WHOIS scope but nothing about the domain string format or whether it accepts subdomains/IDN, so the baseline 3 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+resource (checks whether a domain is available for registration) and immediately scopes it with 'not limited to your own domains', which cleanly distinguishes it from the sibling get_domains that operates on the account's own domains. An agent can route to it 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?

The parenthetical 'nicht auf eigene Domains beschränkt' gives a clear condition for choosing this over the account-scoped domain tools. It stops short of naming the nearest alternative (suggest_domain_alternatives) or stating when-not to use it, so it is clear context without explicit routing.

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