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

readOnlyHint=true already tells the agent this is a safe read. The description adds the meaningful context that the result reflects sending reputation, but omits rate limits, data source, and whether lookups fail for unresolvable or newly-registered domains.

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?

One front-loaded sentence stating the resource and return fields, with the motivating context in a compact parenthetical. Nothing is wasted, though the sentence could carry a bit more routing value without bloat.

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 annotations covering safety and no output schema, the description adequately conveys what is returned (registration date, age) and why it matters. Only the overlap with whois_lookup and failure modes are unaddressed.

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 'domain' parameter with 100% schema description coverage ('Domain, e.g. example.com'), so the schema fully carries parameter meaning. The description adds no format, TLD, or input-validation guidance beyond it, making the baseline 3 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?

The description states a specific verb ('Get') and resource ('a domain's registration date and age'), so the agent knows exactly what comes back. It doesn't explicitly distinguish itself from the sibling whois_lookup, which likely overlaps in scope, 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?

The parenthetical about young domains having weak sending reputation implies a use case (email deliverability/sender reputation checks), but there is no explicit when-to-use, when-not-to-use, or named alternative such as whois_lookup. Usage is only inferable.

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