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

Annotations already declare readOnly, idempotent, non-destructive and openWorld, so the safety profile is covered. The description adds genuinely useful context on top: a live registry/RDAP source, an explicit privacy guarantee ('Personal details of the holder are never returned'), and an outbound link to the explained record.

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?

Two front-loaded sentences with no filler; the capability and the privacy caveat come first. The trailing 'Links to the explained record on hivex.si' reads slightly promotional and is partly redundant given an output schema exists, which keeps it from a 5.

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?

An output schema exists, so return structure need not be documented, and the description still enumerates the salient fields and adds a privacy guarantee. For a single-parameter read-only lookup with full annotation coverage, an agent has everything it needs to call it correctly.

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 one required parameter with 100% schema description coverage, including the note that a hostname is reduced to its domain. The description adds nothing to the parameter beyond 'any domain', so the schema carries the load and the baseline of 3 applies.

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 precise verb and resource ('look up the registration record of any domain') plus the data source ('live from its registry's RDAP'), which cleanly separates it from a DNS-resolution sibling. It does not name check_name, dns_lookup or find_names, so sibling differentiation remains implicit rather than explicit.

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 stated outputs (registration status, registrar, dates, status codes, name servers) imply when to reach for it, but there is no explicit when-not-would-be-better guidance and no alternative tool named. Usage is inferable, not spelled out.

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