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

With no annotations provided, the description carries the full burden. It successfully discloses the behavioral trade-off between speed and accuracy (DNS_ONLY vs DNS_AND_WHOIS) and identifies the external provider (WhoisXML). However, it lacks details on return value structure, error conditions, or rate limiting.

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?

The description is a single, efficient sentence that front-loads the primary action ('Check if a domain name is available'). The em-dash cleanly separates the core purpose from implementation details (check methods and provider). No words are wasted.

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?

Given the low complexity (2 parameters, simple boolean/conceptual output) and 100% schema coverage, the description is appropriately complete. It explains the essential behavioral distinction between modes. A score of 5 would require details on return format or error handling, which are absent but not strictly necessary given the lack of output schema.

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?

With 100% schema description coverage, the baseline is 3. The description adds value by semantically enriching the 'mode' parameter, describing DNS_ONLY as 'fast' and DNS_AND_WHOIS as 'thorough' and 'more accurate,' which helps the agent make informed parameter choices beyond the schema's technical enum labels.

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 provides a specific verb ('Check'), clear resource ('domain name'), and distinct scope ('available for registration'). It effectively distinguishes from siblings like 'whois.domain.lookup' (which retrieves WHOIS records) by focusing on registration availability, and notes the specific data provider (WhoisXML).

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 description provides clear context for selecting between the two modes by framing them as 'fast DNS check' versus 'thorough DNS+WHOIS verification' (more accurate). While it doesn't explicitly name sibling alternatives, the specific focus on 'availability for registration' provides sufficient context for selection.

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