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

With no annotations, the description carries the full burden and does well: it discloses the mechanism ('Reine DNS-Abfrage') and an important safety trait ('kein Mailversand'), so the agent knows this is a non-destructive lookup that touches no third party. It stops short of covering rate limits, caching, or how many variants are probed.

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 sentences, each earning its place: what is generated and checked, why the result matters, and the safety disclaimer. The core action is front-loaded with no filler or repetition.

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 one-parameter tool with no output schema and no annotations, the description conveys both the process and the shape of the result (registered status plus mail-server presence), which is enough for correct invocation. Only minor gaps remain around result volume and error behaviour.

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 coverage is 100% and the single parameter is fully documented there (including the email/URL reduction behaviour), so the baseline is 3. The description adds the notion that variants are derived from the given domain but no additional syntax, format, or constraint detail beyond the schema.

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 multi-step verb chain: it generates typo/character-swap/umlaut/ending variants of a domain and DNS-checks which are registered and whether they run a mail server. That is far more specific than a generic 'check domain'. It does not, however, name or distinguish itself from the closest siblings (dns_check, domain_haertung, spoofing_check), so it falls 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?

Usage is implied rather than stated: the note that mail-server domains are suitable for CEO fraud signals this is a typosquatting/phishing-risk assessment tool, which gives the agent a context to invoke it. There is no explicit when-to-use, when-not-to-use, or routing to alternatives such as dns_check or domain_haertung.

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