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

With no annotations, the description carries the full burden of behavioral disclosure. It does well by enumerating the exact output fields (status, TLD type, WHOIS/RDAP servers, etc.) and adding the 'Cost = 1 token' note. It does not mention auth requirements or rate limits, but for a read-only lookup this is acceptable. The description adds substantial behavioral context beyond the schema.

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 perfectly sized and front-loaded. The first sentence states the purpose, followed by a compact list of return fields, an input rule, and a cost note. Every sentence earns its place; no filler or unnecessary detail.

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 a simple one-parameter tool with an output schema and full schema coverage, the description covers the essentials: what it returns, how to format the input, and the cost. It lacks explicit mentions of error conditions or data availability, but these are not critical for a single-TLD lookup and are unlikely to impede selection or invocation.

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. The description reinforces the parameter meaning ('without a leading dot') and adds one more example ('com'), but this is redundant with the schema's own description. No significant additional meaning is provided beyond what the schema already says.

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 uses a specific verb ('Look up') and a precise resource ('detailed registry information for a single top-level domain'). It clearly distinguishes this tool from siblings by emphasizing 'single TLD' and 'detailed registry information', which separates it from domains.whois or domains.rdap. The tool's scope is unmistakable.

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 when to use the tool: when you need comprehensive registry details for a single TLD. It also gives an explicit input rule ('without a leading dot'). However, it does not explicitly compare with alternatives like domains.whois or domains.rdap, so it lacks explicit exclusions or when-not guidance.

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