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

The annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered, and the description adds genuinely useful disclosure the annotations do not carry: a per-call price of $0.003 USDC via x402, plus the underlying data sources (RDAP/WHOIS, DNS, HTTPS probe). It omits what happens on a non-existent/unregistered domain and any rate or failure behavior, 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, front-loaded with the purpose then the return inventory, closing with the cost. No filler or restatement of the tool name.

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?

There is no output schema, so the enumeration of returned fields is doing necessary work and is reasonably thorough; the cost is also disclosed. It stops short of describing the response shape or behavior for unavailable domains, so an agent still lacks a little detail.

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?

One parameter with 100% schema description coverage ('e.g. example.com'), so the schema carries the burden. The description adds nothing about the domain argument — e.g. whether a subdomain, IDN, or bare name is accepted — 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?

States the verb and resource ('Domain lookup') and then enumerates the specific data returned: availability, registrar, created/expiry dates, nameservers, A/AAAA/MX/NS/TXT records, and HTTPS reachability. This makes it distinguishable from the narrower 'dns' sibling in practice. It falls short of a 5 because no sibling (dns, domain_audit) is named or explicitly ruled out.

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?

No when-to-use condition, no prerequisites, and no alternatives are offered ('use dns for records only, domain_audit for a full audit' would be the natural routing). The only practical guidance is the cost line, which is cost transparency rather than usage guidance.

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