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

Annotations already declare readOnly and non-destructive semantics, so the description's job is narrower. It adds interpretive value by explaining what the result means for deliverability. It omits edge behavior for unregistered, private, or unsupported-TLD domains, which keeps it from a 5.

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?

A single sentence with the concrete return values front-loaded and the parenthetical earning its place by telling the agent why the result matters. No filler.

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 read tool with full schema coverage, the description is nearly sufficient and partly compensates for the missing output schema by naming the returned values. The remaining gap is behavior on missing or private WHOIS data and how this differs from the check_* siblings.

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?

Only one parameter exists and the schema documents it fully with an example format, so the baseline is 3. The description adds no format, normalization, or subdomain-handling detail beyond the schema's example.

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 (get) and resource (domain age) and names the concrete outputs: registration date and age. It stops short of differentiating from the sibling whois_lookup, which plausibly also surfaces registration data, so an agent cannot route between the two on description alone.

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 'young domains have weak sending reputation' implies the tool is for sender-reputation assessment, which gives the agent a usage context. There is no explicit when-to-use/when-not guidance and no mention of whois_lookup as the alternative for broader registration data.

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