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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so the safety profile is covered. The description adds genuinely new context beyond the annotations: the data comes from the official RDAP registry rather than scraped WHOIS, and it explicitly returns 'No personal contact data', which sets expectations about result contents and privacy.

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 front-loading is good, but the second sentence 'Domain info.' is pure redundancy after the title and first sentence, and the parenthetical '(WHOIS/RDAP)' is repeated from the title. The remaining content is dense and earns its place, but those wasted fragments drag the structure down.

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?

With no output schema, the description usefully enumerates the returned fields (registrar, created, expiry, age, status, nameservers) and the data source, which is what an agent needs to know it is the right tool. It omits what happens for an unregistered or invalid domain (error vs. empty result), the one behavioral gap for a lookup tool.

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 parameter with 100% schema description coverage (type plus an example, 'apify.com'), so the schema already carries the semantics. The description adds no extra guidance on accepted formats (subdomains, IDN, trailing dots), so the baseline 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?

It names a specific resource and enumerates exactly what it retrieves (registrar, creation date, expiry, age, status, nameservers) and the underlying data source (RDAP). However, the opening line 'Is a domain registered?' overlaps with the sibling domain_availability, and the description never draws that boundary, so an agent could pick the wrong tool for a pure availability check.

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 list of questions ('Who is the registrar, when was it created, when does it expire') implies the use case clearly enough to invoke it, but there is no explicit when-to-use versus domain_availability or dns_lookup, and no stated exclusions or prerequisites.

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