Whois lookup over RDAP: registrar, registrant, created, expires, nameservers.
Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.
{
"id": 1,
"jsonrpc": "2.0",
"method": "tools/call",
"params": {
"arguments": {
"domain": "<domain>"
},
"name": "whois_lookup"
}
}| Name | Required | Description | Default |
|---|---|---|---|
| domain | Yes | Domain to look up |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden, and it does disclose the underlying protocol (RDAP) and the shape of the returned record, which is genuinely useful behavior beyond the schema. It omits important operational traits such as rate limits, TLD/registry coverage, and what happens for unregistered or private-registration 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?
A single tight clause front-loads the operation and protocol, followed by the return fields; there is no filler or redundancy. Every element earns its place.
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 lookup with no output schema, listing the arbitrary returned fields is exactly the compensation needed, so an agent can use the result without guessing. The remaining gap is sibling disambiguation against the 'whois' tool and error/not-found behavior.
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 required 'domain' parameter with 100% schema description coverage, so the schema already carries full parameter semantics and the baseline is 3. The description adds no format hints (e.g. whether to pass a bare name or a URL, IDN handling) beyond what the schema states.
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 names a specific verb and resource ('Whois lookup over RDAP') and enumerates the data returned (registrar, registrant, created, expires, nameservers), so an agent knows exactly what it gets. It does not, however, distinguish itself from the sibling tool 'whois' or from adjacent lookups like dns_lookup and ip_lookup.
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 guidance and no alternatives are named, even though the sibling list contains a near-identical 'whois' tool plus dns_lookup and ip_lookup. The agent must infer from the name alone when this is preferable to the plain whois sibling.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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